[AArch64][GlobalISel] Push ADD/SUB through Extend Instructions (#90964)

The regression in one test is due to a SUB instruction being pushed
through the extend, leaving behind the abs instruction, which prevents
it from selecting uabdl instructions shown below:

`i32 abs(i32 sub(i32 ext i8, i32 ext i8))` => 
`i32 abs(i32 ext(i16 sub(i16 ext i8, i16 ext i8)))`

This is intended to be fixed in a follow up patch