Implement full .errors verification in tests

[RossPatterson]

In grammars-v4 issue 2821, I wrote:

I'm experimenting now with making trgen verify ... the .errors reference files, as antlr4test-maven-plugin does in AssertErrorsErrorListener ... I'm interested in the .errors capability because it seems like it should be fully supported.

As I said, I've got an experiment in progress to do this.

[teverett]

@RossPatterson this is great news. Thank-you!

[RossPatterson]

I encountered the grammars-v4/csharp example issue-2612 error described in antlr4 issue #3700 during work on this. I expect I'll have to add it to grammars-v4/_scripts/skip_csharp.txt.

[RossPatterson]

At this point, I believe this work is complete, and PR #2855 is ready to merge.

• The build-csharp CI job now skips csharp, due to antlr4 issue #3700.
• The build-php CI job now skips logo/logo, due to issue [logo/logo] Unexpected error from example logo_feature_butfail_2.txt #2859.
• The build-php CI job and all JavaScript build-pwsh CI jobs now skip python/python3alt, as it has Java code in the @members sections. All other non-Java builds already skipped it.
• All test drivers (e.g., _scripts/*/Program.*) now dump out the detected errors to stdout in the expected format, and only dump the parse tree if there are no errors.
• All test scripts (i.e., _scripts/*/test.sh, _scripts/*/tester.psm1) now check the detected errors against the reference files, and only check the parse tree if there are no errors.
• The Java test driver now dumps out the errors in UTF-8. All the other test drivers already did so.
• All the non-skipped grammars that have .errors files in their examples directory generate all and only those errors.
• All non-skipped tests are succeeding.