API: added array
Adds

- a new top-level `pd.array` method for creating arrays
- all our extension dtypes to the top-level API
- adds pd.arrays for all our EAs

TODO

- [x] Add the actual array classes somewhere to the public API (pandas.arrays?)
- [x] API docs for the rest of the arrays and dtypes.

Closes #22860 

supersedes #23532.