[mlir][vector] Add canonicalzation pattern for shape_cast(create_mask)

This is primarily to avoid trailing unit dims:
```
%1 = vector.create_mask %c1, %dim_0, %c1, %c1 : vector<1x4x1x1xi1>
%2 = vector.shape_cast %1 : vector<1x4x1x1xi1> to vector<1x4xi1>
```
becomes:
```
%1 = vector.create_mask %c1, %dim_0 : vector<1x4xi1>
```

Differential Revision: https://reviews.llvm.org/D158111