make jnlp build process runnable again

[ebarboni]

kind of the opposite of #9312

I do not remember if it was possible to generate a NetBeans jnlp back in the day.
ant build-jnlp build only the different modules

this seems to work to rebuild jnlp files. this is quite long (20minutes)

the sha1 is not working anymore so need a bump to sha256
jnlp.verify.exclusion updated to match what ant warns about.

Some late verification like this one are failling (jarsigner also say so):

<testcase classname="org.netbeans.nbbuild.VerifyJNLP" name="/home/barboni/fork/netbeans/netbeans/nbbootstrap/netbeans/nbbuild/build/jnlp/org-eclipse-core-contenttype.jnlp/testSignatures" time="0.0">
<failure message="error examining signatures in /home/barboni/fork/netbeans/netbeans/nbbootstrap/netbeans/nbbuild/build/jnlp/org-eclipse-core-contenttype/org-eclipse-core-contenttype.jar: java.lang.SecurityException: invalid SHA1 signature file digest for org/eclipse/core/internal/content/XMLRootHandler$StopParsingException.class" type="junit.framework.AssertionFailedError">error examining signatures in /home/barboni/fork/netbeans/netbeans/nbbootstrap/netbeans/nbbuild/build/jnlp/org-eclipse-core-contenttype/org-eclipse-core-contenttype.jar: java.lang.SecurityException: invalid SHA1 signature file digest for org/eclipse/core/internal/content/XMLRootHandler$StopParsingException.class</failure>
</testcase>

[ebarboni]

I have no clue, why I need to use classpath="${cp.extra}" to make it work

[mbien]

do we know if a minimal platform app would still start using webstart?

with the JDK removing SecurityManager (24) and AppContext (seems to happen now with 27), my guess is that the only LTS JDK where this still might work and we still support would be 21.

(I have nothing against fixing it if its not that much work and do a few releases with it fixed)