Add additional logic to CallHierarchyCore.getCompilationUnitNode()

[jjohnstn]

• add check for class file to avoid checking for a java file name which won't find the .java extension and will return false
• fixes Outgoing call hierarchy for methods in classes in a jar with attached source doesn't work since 4.40 #3015

What it does

See issue.

How to test

Run jdt.ls test mentioned in issue.

Author checklist

• I have thoroughly tested my changes
• The change is following the coding conventions
• I have signed the Eclipse Contributor Agreement (ECA)

[arcivanov]

Since this regression was introduced by my PR #2881, I've prepared a regression test for this fix. The test creates a class folder with attached source, verifies the member is an IClassFile with a non-null buffer, and asserts that the outgoing callee hierarchy returns the expected callees via the Java AST path.

Commit: arcivanov@cc39ae870f

Feel free to cherry-pick or squash it into this PR. I couldn't push directly to your fork.

[datho7561]

This fixes the problem for me.

I think it'd be helpful to add the regression test that Arcadiy suggested.

[jjohnstn]

This fixes the problem for me.

I think it'd be helpful to add the regression test that Arcadiy suggested.

Will do.