[ty] Handle field specifier functions that accept `**kwargs` and recognize metaclass-based transformers as instances of `DataclassInstance` (#22018)
## Summary
This contains two bug fixes:
- [Handle field specifier functions that accept
`**kwargs`](https://github.com/astral-sh/ruff/commit/ad6918d505a40b0c87528913a912ee2026b08eb0)
- [Recognize metaclass-based transformers as instances of
`DataclassInstance`](https://github.com/astral-sh/ruff/commit/1a8e29b23c8405fce9c9e07dd48411b877170f6a)
closes https://github.com/astral-sh/ty/issues/1987
## Test Plan
* New Markdown tests
* Made sure that the example in 1987 checks without errors