Add support for float mask to aten::masked_fill

[gpetters94]

This adds a few small changes that are needed for OPT support, namely:

• Support for aten::view when the output shape is statically known

• Folding away torch::type_as when both arguments are the same type

• Support for torch::masked_fill when the mask is a float type

[ramiro050]

Can you split the changes into 3 PRs? They are all quite independent from one another. It would also make the commit titles a lot more descriptive, since each PR could get as a title the description you have in the bullet points above.

[gpetters94]

I've split the PRs, this one is for masked_fill now.