[mlir][Vector] Add transformation + pattern to split vector.transfer_read into full...

[mlir][Vector] Add transformation + pattern to split vector.transfer_read into full and partial copies.

This revision adds a transformation and a pattern that rewrites a "maybe masked" `vector.transfer_read %view[...], %pad `into a pattern resembling:

```
   %1:3 = scf.if (%inBounds) {
      scf.yield %view : memref<A...>, index, index
    } else {
      %2 = vector.transfer_read %view[...], %pad : memref<A...>, vector<...>
      %3 = vector.type_cast %extra_alloc : memref<...> to
      memref<vector<...>> store %2, %3[] : memref<vector<...>> %4 =
      memref_cast %extra_alloc: memref<B...> to memref<A...> scf.yield %4 :
      memref<A...>, index, index
   }
   %res= vector.transfer_read %1#0[%1#1, %1#2] {masked = [false ... false]}
```
where `extra_alloc` is a top of the function alloca'ed buffer of one vector.

This rewrite makes it possible to realize the "always full tile" abstraction where vector.transfer_read operations are guaranteed to read from a padded full buffer.
The extra work only occurs on the boundary tiles.

Differential Revision: https://reviews.llvm.org/D84631