[llvm] [GlobalISel] Check width of APInts in Reassoc PtrAdd combine (PR #84335)

[Jay Foad via llvm-commits]

jayfoad wrote:

Allowing arbitrary widths for the RHS of G_PTR_ADD makes me very uncomfortable. I would much prefer enforcing that the RHS has the same bitwidth as the index size of the pointer's address space. See also #81473.

https://github.com/llvm/llvm-project/pull/84335