false positive contradictory null annotations since 2024-03

[stephan-herrmann]

fixes #2178

includes updates to enable using jclMin21.jar + src.zip

Also AbstractJavaModelTests was not ready for use the library stub, but that was needed for the test to trigger this bad path:

• we add a synthetic "import static java.lang.StringTemplate.STR" with null annotations temporarily disabled
• while resolving the field we need to resolve type java.lang.String
• due to java/lang/String.eea we decorate a string method with @NonNull
• this triggers the initial load of the NonNull annotation type
• since null annotations are temporarily disabled, we skip the following assignment inside PackageBinding.checkIfAnalysisAnnotationType():
  type.typeBits |= TypeIds.BitNonNullAnnotation;
• ergo: org.eclipse.jdt.annotation.NonNull is not known as a null annotation from which various "interesting" effects could follow.

I relation to #1513 (comment) I chose the second option:

... to encapsulate all fields of ImportBinding, so that we can use lazy initialization, but that would affect all locations accessing this class, so not a tiny change.

With that change, disabling null annotations (the "kludge" from #1513) is no longer necessary, the field STR is resolved only when needed, which restores proper null analysis.