As part of this extension this change also does some general cleanup
1) Make all the methods take `RewriterBase` as arguments instead of
creating their own builders that tend to crash when used within
pattern rewrites
2) Split `coalesePerfectlyNestedLoops` into two separate methods, one
for `scf.for` and other for `affine.for`. The templatization didnt
seem to be buying much there.
Also general clean up of tests.
5aeb604c7c