[MLIR] Introduce flag -print-ngraph-ir-after-all. (#3457)
[MLIR] Introduce flag -print-ngraph-ir-after-all. (#3457)

This PR is a stepping stone towards unifying nGraph MLIRCompiler printing
flags with those used in MLIR. It enables flag -print-ir-after-all
implemented in MLIR pass manager and adds flag -print-ngraph-ir-after-all
to MLIRCompiler so that we can use it to dump IR for those transformations
that we do directly in MLIRCompiler without using a proper pass. Eventually,
everything should be working as a pass and the nGraph variant of the
flag shouldn't be needed. NGRAPH_MLIR_DUMP_ALL macro is no longer
needed.
NervanaSystems/ngraph,NervanaSystems/ngraph,NervanaSystems/ngraph,NervanaSystems/ngraph