Hint/test stabilization: cannot keep TypeMirrors across javac context invocations.

[lahodaj]

Seeing the failure here:
https://github.com/apache/netbeans/actions/runs/19711486484/attempts/1#summary-56473993246

it reminded me a similar problem elsewhere, so I took a look at the hint. In general, hint analysis and fix application may run in different javac contexts (different javac instances). It probably does not happen commonly, but it might, and it most likely happened in the test run above. And the Fix is keeping a TypeMirror from the analysis javac context, and tries to work with in the application context, which fails.

This PR is handling that using a TypeMirrorHandle.

As a follow-up work, we could try to enhance the test frameworks to always use a different javac instance for analysis and fix application, to avoid trouble like this.

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[mbien]

great find!

[matthiasblaesing]

This looks suspiciously like a similar problem in PR #9005. @lahodaj would you mind having a look at that PR?