Note that at the current moment, the newly-introduced
`SparseTensorLevel` classes are far from complete, we plan to migrate
code generation related to accessing sparse tensor levels to these
classes in the near future to simplify `LoopEmitter`.
Separates actual transformation files from supporting utility files in
the transforms directory. Includes a bazel overlay fix for the build (as
well as a bit of cleanup of that file to be less verbose and more
flexible).
