Rename publishM2Local to publishLocal, remove old ~/.ivy2 publishLocal implementation

[lihaoyi]

Follow up to recent work to get rid of legacy ivy terminology (e.g. #4930), we should publish to the local ~/.m2 maven repo rather than ~/.ivy2 ivy repo by default.

[lefou]

IMHO, we should keep support for publishing to the local ivy repo for a while, maybe as publishIvyLocal. I think sbt is still using it.

Also, why not keep the name publishM2Local. Since there are multiple local repository standards, being more explicit leaves less room for confusion.

(Ideally, publishLocal would just be an alias to the concrete publish method and defaults to publishM2Local.)

[alexarchambault]

About using ~/.m2/repository, there have been issues when using this repository in coursier see here and the links there.

But a Mill-specific local Maven repository could work, like ~/.mill/maven-local. I think I could add it as a default in coursier (alongside ~/.ivy2/local), and we could give instructions to Maven / Gradle users about how to use it in these.