Allows deferred location attribute in `parseOptionalLocationSpecifier`

[mehdi_amini]

Summary

Before this patch, deferred location in operation like test.pretty_printed_region would
break the parser, and so the IR round-trip.

Depends On D117088

[rriddle]

mlir/lib/Parser/Parser.cpp

344–347

1757–1758

1803–1804

Is this ever false now?

[mehdi_amini]

Rebase

[mehdi_amini]

mlir/lib/Parser/Parser.cpp

1803–1804

I don't think so! This is also in the parent revision, I fixed it there

[rriddle]

LG