j2pyi: More improvements

[mikehearn]

Description

This PR fixes various issues in the pyinterfacegen module and makes usability improvements:

• Improves the README.
• You can now explicitly specify with globs and regex what other packages you expect to be typed. Anything that doesn't match will be emitted as untyped. This works better than trying to guess based on dependencies as e.g. the JDK doesn't come with Python type stubs!
• Refactored the code by splitting parts out to a separate utility file.
• Fixed various bugs especially around generics and overload emission, where there have been a lot of edge cases and issues.

How Has This Been Tested?

With these changes I can generate and type check .pyi stubs for quite sophisticated Java modules like Micronaut Core.

I test with the unit tests and by using the typecheckApacheCommonsStubs Gradle task.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[olyagpl]

JavaDoc -> Javadoc
For consistency :)