[GlobalISel] Narrow binops feeding into G_AND with a mask

This is a fairly common pattern:

```
%mask = G_CONSTANT iN <mask val>
%add = G_ADD %lhs, %rhs
%and = G_AND %add, %mask
```

We have combines to eliminate G_AND with a mask that does nothing.

If we combined the above to this:

```
%mask = G_CONSTANT iN <mask val>
%narrow_lhs = G_TRUNC %lhs
%narrow_rhs = G_TRUNC %rhs
%narrow_add = G_ADD %narrow_lhs, %narrow_rhs
%ext = G_ZEXT %narrow_add
%and = G_AND %ext, %mask
```

We'd be able to take advantage of those combines using the trunc + zext.

For this to work (or be beneficial in the best case)

- The operation we want to narrow then widen must only be used by the G_AND
- The G_TRUNC + G_ZEXT must be free
- Performing the operation at a narrower width must not produce a different
  value than performing it at the original width *after masking.*

Example comparison between SDAG + GISel: https://godbolt.org/z/63jzb1Yvj

At -Os for AArch64, this is a 0.2% code size improvement on CTMark/pairlocalign.

Differential Revision: https://reviews.llvm.org/D107929