[MPS] Fix nn.functional.conv_transpose2d grad (#94871)
- add _mps_convolution_impl that takes optional shape
- for conv_tranpose2d grad, use the shape from forward pass directly
- for conv, calculate the shape from input
- remove nn.functional.conv_transpose2d grad from blocklist
Pull Request resolved: https://github.com/pytorch/pytorch/pull/94871
Approved by: https://github.com/kulinseth
