[mlir][OpDSL] Fix OpDSL tests after https://reviews.llvm.org/D114680.

Update the shapes of the convolution / pooling tests that where detected after enabling verification during printing (https://reviews.llvm.org/D114680). Also split the emit_structured_generic.py file that previously contained all tests into multiple separate files to simplify debugging.

Reviewed By: stellaraccident

Differential Revision: https://reviews.llvm.org/D114731