fix: localized array,group,blocks fields duplicate with empty values (#15849)

### What?
  Localized blocks, array, and group fields are empty when           
  duplicating a selected locale.

### Why?
filterDataToSelectedLocales assumed field types (blocks,
  array, group) always stored data directly as arrays. When
  these fields are localized, data is wrapped in a locale map ({ en:
  [...], de: [...] }), which was not being unwrapped before
  processing.

### How?
 - Added locale-aware branching for blocks, array, and group field
  types — when the field is localized, the locale map is filtered
  first, then each locale's value is recursed into
  - Extracted a filterLocaleMap helper to consistently filter and
  transform locale maps across all field types
  - Added unit tests

Fixes #15847

---------

Co-authored-by: pevecj <jakob.pevec@renderspace.si>

Author: jakobpevec

packages/payload/src/utilities/filterDataToSelectedLocales.spec.ts

@@ -111,6 +111,7 @@ describe('filterDataToSelectedLocales', () => {
         configBlockReferences: [
           {
             slug: 'content',
+            flattenedFields: [],
             fields: [
               {
                 name: 'body',
@@ -140,6 +141,245 @@ describe('filterDataToSelectedLocales', () => {
     })
   })
 
+  describe('localized arrays', () => {
+    it('should filter localized array to selected locales and recurse into rows', () => {
+      const fields: Field[] = [
+        {
+          name: 'items',
+          type: 'array',
+          localized: true,
+          fields: [
+            {
+              name: 'title',
+              type: 'text',
+            },
+          ],
+        },
+      ]
+
+      const docWithLocales = {
+        items: {
+          en: [{ title: 'English Item' }],
+          es: [{ title: 'Spanish Item' }],
+          de: [{ title: 'German Item' }],
+        },
+      }
+
+      const result = filterDataToSelectedLocales({
+        configBlockReferences: [],
+        docWithLocales,
+        fields,
+        selectedLocales,
+      })
+
+      expect(result.items).toEqual({
+        en: [{ title: 'English Item' }],
+      })
+    })
+
+    it('should handle non-localized array with localized children', () => {
+      const fields: Field[] = [
+        {
+          name: 'items',
+          type: 'array',
+          fields: [
+            {
+              name: 'label',
+              type: 'text',
+              localized: true,
+            },
+            {
+              name: 'value',
+              type: 'text',
+            },
+          ],
+        },
+      ]
+
+      const docWithLocales = {
+        items: [
+          { label: { en: 'English', es: 'Spanish' }, value: 'one' },
+          { label: { en: 'English 2', es: 'Spanish 2' }, value: 'two' },
+        ],
+      }
+
+      const result = filterDataToSelectedLocales({
+        configBlockReferences: [],
+        docWithLocales,
+        fields,
+        selectedLocales,
+      })
+
+      expect(result.items).toEqual([
+        { label: { en: 'English' }, value: 'one' },
+        { label: { en: 'English 2' }, value: 'two' },
+      ])
+    })
+  })
+
+  describe('localized blocks', () => {
+    it('should filter localized blocks field to selected locales', () => {
+      const fields: Field[] = [
+        {
+          name: 'layout',
+          type: 'blocks',
+          localized: true,
+          blocks: [
+            {
+              slug: 'hero',
+              fields: [
+                {
+                  name: 'heading',
+                  type: 'text',
+                },
+              ],
+            },
+          ],
+        },
+      ]
+
+      const docWithLocales = {
+        layout: {
+          en: [{ blockType: 'hero', id: '1', blockName: 'Hero EN', heading: 'Hello' }],
+          es: [{ blockType: 'hero', id: '2', blockName: 'Hero ES', heading: 'Hola' }],
+          de: [{ blockType: 'hero', id: '3', blockName: 'Hero DE', heading: 'Hallo' }],
+        },
+      }
+
+      const result = filterDataToSelectedLocales({
+        configBlockReferences: [],
+        docWithLocales,
+        fields,
+        selectedLocales,
+      })
+
+      expect(result.layout).toEqual({
+        en: [{ blockType: 'hero', id: '1', blockName: 'Hero EN', heading: 'Hello' }],
+      })
+    })
+
+    it('should filter localized blocks with multiple selected locales', () => {
+      const fields: Field[] = [
+        {
+          name: 'layout',
+          type: 'blocks',
+          localized: true,
+          blocks: [
+            {
+              slug: 'text',
+              fields: [
+                {
+                  name: 'body',
+                  type: 'text',
+                },
+              ],
+            },
+          ],
+        },
+      ]
+
+      const docWithLocales = {
+        layout: {
+          en: [{ blockType: 'text', id: '1', blockName: 'Text EN', body: 'English' }],
+          es: [{ blockType: 'text', id: '2', blockName: 'Text ES', body: 'Spanish' }],
+          de: [{ blockType: 'text', id: '3', blockName: 'Text DE', body: 'German' }],
+        },
+      }
+
+      const result = filterDataToSelectedLocales({
+        configBlockReferences: [],
+        docWithLocales,
+        fields,
+        selectedLocales: ['en', 'es'],
+      })
+
+      expect(result.layout).toEqual({
+        en: [{ blockType: 'text', id: '1', blockName: 'Text EN', body: 'English' }],
+        es: [{ blockType: 'text', id: '2', blockName: 'Text ES', body: 'Spanish' }],
+      })
+    })
+  })
+
+  describe('localized groups', () => {
+    it('should filter localized group to selected locales and recurse into children', () => {
+      const fields: Field[] = [
+        {
+          name: 'meta',
+          type: 'group',
+          localized: true,
+          fields: [
+            {
+              name: 'title',
+              type: 'text',
+            },
+            {
+              name: 'description',
+              type: 'text',
+            },
+          ],
+        },
+      ]
+
+      const docWithLocales = {
+        meta: {
+          en: { title: 'English Title', description: 'English Desc' },
+          es: { title: 'Spanish Title', description: 'Spanish Desc' },
+          de: { title: 'German Title', description: 'German Desc' },
+        },
+      }
+
+      const result = filterDataToSelectedLocales({
+        configBlockReferences: [],
+        docWithLocales,
+        fields,
+        selectedLocales,
+      })
+
+      expect(result.meta).toEqual({
+        en: { title: 'English Title', description: 'English Desc' },
+      })
+    })
+
+    it('should handle non-localized group with localized children', () => {
+      const fields: Field[] = [
+        {
+          name: 'seo',
+          type: 'group',
+          fields: [
+            {
+              name: 'title',
+              type: 'text',
+              localized: true,
+            },
+            {
+              name: 'slug',
+              type: 'text',
+            },
+          ],
+        },
+      ]
+
+      const docWithLocales = {
+        seo: {
+          title: { en: 'English SEO', es: 'Spanish SEO' },
+          slug: 'my-page',
+        },
+      }
+
+      const result = filterDataToSelectedLocales({
+        configBlockReferences: [],
+        docWithLocales,
+        fields,
+        selectedLocales,
+      })
+
+      expect(result.seo).toEqual({
+        title: { en: 'English SEO' },
+        slug: 'my-page',
+      })
+    })
+  })
+
   describe('simple fields', () => {
     it('should filter localized field values to selected locales', () => {
       const fields: Field[] = [