Reworked some BSP module inspection tasks

[lefou]

This should improve (fix) performance and OOM issues with large multi module projects where modules depend heavily on each other.

bspCompileClassesPath and bspCompileClasspath are now Targets instead of Tasks. This makes them cacheable and also easier to override in derived modules. I also changed the logic in some transitiveXXX targets from a recursive call to all dependencies to just calling the non-recursive target on a transitive modules list. This should mitigate OOM issue as reported here: #1792 (comment)

Fix #1792

Supersedes #1794

[lefou]

Turns out, Mill's compileModuleDeps handling was a bit sloppy. The calclulation of the transitive module dependencies also included transitive compile-only dependencies, which should have never end up in. My change fixed that. As a result, I needed to correct our build.sc and add some dependencies, to make the self-bootstrap tests succeed.

[lolgab]

@lefou There is a bug in mill-mima that ignores the mimaExcludeAnnotations. I reproduced it in a test but the implementation seems exactly the same as Sbt MiMa so I couldn't understand why it doesn't work.
I'm now trying to call MiMa from an insulated classloader to see if the problem is related to the classpath.
In the meantime, the only workaround is to manually add excludes as you did.

Opened an issue here: lolgab/mill-mima#41