_isHostProvided is not initialized when using --map for async WIT resources

[ritalin]

Related to #1313, but this issue is about missing initialization of _isHostProvided.

When mapping a JS class as an async WIT resource using the --map option, _isHostProvided is not initialized.

In contrast, when using --instantiation, _isHostProvided is initialized correctly.

Even if issue #1313 is fixed, _isHostProvided remains undefined for JS class.
As a result, the following branch is never taken:

if (hostProvided) {
  task.resolve([ret]);
  endCurrentTask(0, task.id());
  return task.completionPromise();
}

Actual behavior:

• Since _isHostProvided is not initialized, hostProvided is always falthy (e.g. undefined)
• The fast-path branch is never taken
• Execution falls through to the driver loop path, which assumes a Wasm-originated subtask
• However, this call does not originate from Wasm, so no subtask is created
• As a result, subtask lookup returns null or undefined, leading to a runtime error when accessed

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Full discussion (including context and workaround):
#jco > Unexpected error when using async JS types/functions with im