Improvements to the pyinterfacegen tool

[mikehearn]

Misc improvements including:

• POM metadata is now derived from the root pom.xml
• .pyi generation accuracy is much improved with many bug fixes, especially in the area of generics and overloads.
• The j2pyi Gradle plugin now supports running mypy over it, which can detect internal inconsistencies and mistypings.
• Some package namespaces have been fixed.

[mikehearn]

@steve-s The deploy-local-repo script has been tested but I don't know how best to simulate a full release. That might be the best I can do - if there are bugs the release team may need to study the issue further.

How does it look?

[steve-s]

I can confirm that the deployment script also works for me locally without any issues. I skimmed over the artifacts and I think there are some missing bits:

• j2pyi-doclet is missing <name> and <description> in the pom file
• the gradle plugin artifacts are missing <license>, <developers>, and <scm> in their pom files
• the javadoc and sources jars are missing (it's silly, but even if you don't have JavaDoc, AFAIK the jar must be there)

(note: signing is the only bit that we don't do ourselves and the release team takes care of that)

[steve-s]

Also the artifacts are deployed in a new groupId - is that intentional? Can we make them all be in org.graalvm.python like the rest of the artifacts in this repo?

[mikehearn]

@steve-s How does it look now?

[steve-s]

Now the j2pyi-gradle-plugin seems to be missing name and description. Idk if that changed or I missed that when I checked the artifacts last time. Otherwise looks good.

[mikehearn]

Oops, sorry about that. I'm not sure either but I think it didn't have those originally either, good catch.

[steve-s]

Thanks @mikehearn, LGTM. Do you want to rebase before merge?