Migrate build system to Gradle

[kamildoleglo]

For publishing to work we have to decide on the naming of environment variables for plugin signing and uploading, and probably create a GHAction, although it should be similar to the test one, just with different Gradle task and env variables. A test run for this PR can be viewed on my fork.

Despite some file moves showing up pre-commit as moves correctly, after a commit my git treats them as deletion&addition, regardless of the similarity index value. Not sure if and how I can fix that

[wisechengyi]

It appears that it's also removing pants build in the same diff. Do you think it'd be possible to break out the changes into

1. add gradle build
2. remove pants build

so the changes can be more incremental as well as easier to be reviewed.

Mostly a suggestion. If you think it is difficult to do, please kindly ignore.

[tpasternak]

Unfortunately,.github/workflows/build-test-jar.yml is still needed, shouldn't be removed

[tpasternak]

Don't forget about releases :)

[kamildoleglo]

Do you think it'd be possible to break out the changes into

• add gradle build
• remove pants build

Did that, hope I haven't broken anything. Not sure that helped though, the worst thing are file relocations seen as addition/deletion

[wisechengyi]

Do you think it'd be possible to break out the changes into

• add gradle build
• remove pants build

Did that, hope I haven't broken anything. Not sure that helped though, the worst thing are file relocations seen as addition/deletion

Yeah that's what I meant. So feel free to ignore my suggestion if it turns out difficult.

[kamildoleglo]

I've reset to the old branch, because after the rebase and splitting commits, the tests were broken and I couldn't figure out what was wrong, besides the split didn't make this more reviewable. I also added a publishing action, I don't have a way of testing it though. It can only be run manually as of now.

This PR should be (more or less) reviewable @wisechengyi

[kamildoleglo]

Ping @wisechengyi