[CIR] Add canonicalizer for CleanupScopeOp (#191084)
This change adds a canonicalizer for CleanupScopeOp that erases any
cleanup scope with a trivial cleanup region, inlining the contents of
the body region into the block in place of the cleanup scope op. It also
erases any EH-only cleanup scope whose body region contains only a yield
operation, dropping the cleanup region contents even if they were not
trivial because the EH cleanup is not reachable in this case.
Assisted-by: Cursor / claude-4.6-opus-high
