[mlir] Fix dumping invalid ops

This patch fixes the crash when printing some ops (like affine.for and
scf.for) when they are dumped in invalid state, e.g. during pattern
application. Now the AsmState constructor verifies the operation
first and switches to generic operation printing when the verification
fails. Also operations are now printed in generic form when emitting
diagnostics and the severity level is Error.

Reviewed By: rriddle, mehdi_amini

Differential Revision: https://reviews.llvm.org/D117834