Update to RNN documentation (issue #106085) (#106222)
Addresses [issue #106085](https://github.com/pytorch/pytorch/issues/106085).
In `torch/nn/modules/rnn.py`:
- Adds documentation string to RNNBase class.
- Adds parameters to __init__ methods for RNN, LSTM, and GRU, classes.
- Adds type annotations to __init__ methods for RNN, LSTM, and GRU.
In `torch/ao/nn/quantized/dynamic/modules/rnn.py`:
- Adds type specifications to `_FLOAT_MODULE` attributes in RNNBase, RNN, LSTM, and GRU classes.
> This resolves a `mypy` assignment error `Incompatible types in assignment (expression has type "Type[LSTM]", base class "RNNBase" defined the type as "Type[RNNBase]")` that seemed to be a result of fully specified type annotations in `torch/nn/modules/rnn.py`).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/106222
Approved by: https://github.com/mikaylagawarecki
