[mlir] Fixes to hoist padding

Fix the BlockAndValueMapping update that was missing entries for scf.for op's blockIterArgs.
Skip cloning subtensors of the padded tensor as the logic for these is separate.
Add a filter to drop side-effecting ops.

Tests are beefed up to verify the IR is sound in all hoisting configurations for 2-level 3-D tiled matmul.

Differential Revision: https://reviews.llvm.org/D99255