Fixes for #3539--clean up of python3 grammars

[kaby76]

This PR is a fix for #3539, or at least partially. The plan is to make additional changes later on. For now, the focus is making sure we have most of the targets for the python/python3 grammar, and remove as many of the "python3-*" forked grammars. The whole point is to try to get the Python3 grammars in less of a chaotic state, and easier to maintain.

python/python3 grammar

• All tests in examples/ were partitioned into "large/" and "small/" piles because the parser for some targets is slow. It is likely caused by problems in the grammar, but I haven't focused on fixing the grammar yet.
• The Cpp target works. I moved some of the code from the python3-cpp to the target source and deleted the fork.
• The CSharp target works. The source code was reformatted.
• The Dart target works, but ... it is not in the Github Actions CI testing because the Antlr Dart runtime needs to be fixed, likely only when Antlr 4.14.0 is released in the late fall 2023. [Dart] Fix for #4320--export additional types antlr4#4340
• The PHP target does not work.
• The Java target works. No changes.
• The JavaScript target works.
• The Python3 target works. The forked grammar python3-py was deleted.
• The Typescript target works. The original code in python3-ts used a different Antlr4 Typescript runtime. The code now uses the official Antl4 Typescript runtime. Although the code is usable now, there is a minor problem in the API that should be fixed in Antlr 4.14.0. [typescript] Runtime declares CommonToken(source, .....) wrong. antlr4#4318
• The Go target works, but requires a fix to the Go Antlr runtime. [Go] Fix for #4342--EmitToken(token) in Go target needs to be exported antlr4#4343

All other "python3" grammars

• I removed all grammars that added to the confusion and unnecessary maintenance:
  • python3-ts
  • python3-py
  • python3-without-actions
  • python3alt

[teverett]

@kaby76 thanks!