This is a follow-up PR of #169045 and the second part of #179086.
In #179086, we added support for defining regions in Python-defined ops,
but its usefulness was quite limited because we still couldn’t mark an
op as a `Terminator` or `NoTerminator`. In this PR, we port the
`DynamicOpTrait` (introduced on the C++ side for `DynamicDialect` in
#177735) to Python, so we can dynamically attach traits to
Python-defined ops.
