Implement TimedeltaArray._from_sequence
and have both `TimedeltaArray.__new__` and `TimedeltaIndex.__new__` dispatch to it

One test will fail until #23789 is merged.

- [ ] closes #xxxx
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry
