[quant] Subpackage import in nn.quantized (#84141)
Some of the subpackages were not included in the 'torch.nn.quantized'.
That would cause some specific cases fail.
For example, `from torch.nn.quantized import dynamic` would work,
but `import torch; torch.nn.quantized.dynamic` would fail.
Fixes #ISSUE_NUMBER
Pull Request resolved: https://github.com/pytorch/pytorch/pull/84141
Approved by: https://github.com/andrewor14
