Use deeper hierarchies of subprojects and subdirectories

[liblit]

If we have a :foo.bar Gradle subproject and also a :foo.bar.baz Gradle subproject, then perhaps we should move the latter under the former as a :foo.bar:baz sub-subproject, which would also entail renaming the foo.bar.baz subdirectory as foo.bar/baz.

There's a certain hierarchical "everything in its place" appeal to this over the current flat project and directory structure. But it would be huge churn in directories like com.ibm.wala.cast.* and com.ibm.wala.ide.*, so I don't know whether that's justified. I welcome any thoughts from others on this.

In a Slack conversation, @msridhar already commented:

I’m a bit scared about what that might break. And I don’t see a big benefit other than aesthetics and maybe some better shell tab completion. I would open an issue on it so we could discuss before pushing too far.

These are certainly valid concerns, though personally I think that our testing infrastructure is good enough to prevent us from breaking things. The "aesthetics and maybe some better shell tab completion" benefits are valid too, and seem fairly minor. So again, there's a good chance we'll decide that this just isn't sufficiently justified.