Allow the `names` argument in `MatchOp.match_op_names` to be of type
`str` in addition to `Sequence[str]`. In this case, the argument is
treated as a list with one name, i.e., it is possible to write
`MatchOp.match_op_names(..., "test.dummy")` instead of
`MatchOp.match_op_names(..., ["test.dummy"])`.
Reviewed By: ftynse
Differential Revision: https://reviews.llvm.org/D155807
8fd207fd0d