Use the vanniktech plugin to configure Maven publishing

[lppedd]

I've looked at buildSrc, as I'm trying to re-configure to publish also to a private repository, and I think you can simplify the configuration a lot by using https://vanniktech.github.io/gradle-maven-publish-plugin/.

You can take antlr-kotlin as example:
https://github.com/lppedd/antlr-kotlin/blob/7fc16cceaf384d64191f86483bc5692356f6322e/antlr-kotlin-runtime/build.gradle.kts#L51-L61

[sschuberth]

Here is another example use in case it helps.