[mlir][Linalg] Fix padding related bugs.

This revision fixes the fact that the padding transformation did not have enough information to set the proper type for the padding value.
Additionally, the verifier for Yield in the presence of PadTensorOp is fixed to properly report incorrect number of results or operands. Previously, the error would be silently ignored which made the core issue difficult to debug.

Differential Revision: https://reviews.llvm.org/D96264