[MLIR] Modify Partial op conversion mode to optionally track all non-legalizable operations.

There are three op conversion modes: Partial, Full, and Analysis. This change modifies the Partial mode to optionally take a set of non-legalizable ops. If this parameter is specified, all ops that are not legalizable (i.e. would cause full conversion to fail) are tracked throughout the partial legalization.

Differential Revision: https://reviews.llvm.org/D78788