[mlir] make transform interpreter debug spew less verbose

In particular, move the printing of the top-level payload after each
transform under the "full output" debug flag, it is rarely useful and
excessively long. Also don't print the regions of the transform
operation being applied as each individual operation in the region is
likely going to be applied later by itself and therefore printed.

Reviewed By: nicolasvasilache

Differential Revision: https://reviews.llvm.org/D148014