[InstCombine] Refactor folding of commutative binops over select/phi/minmax (#76692)

This patch cleans up the duplicate code for folding commutative binops
over `select/phi/minmax`.

Related commits:
+ select support:
https://github.com/llvm/llvm-project/commit/88cc35b27e6c7966ab2463fa06d3dd970e88df64
+ phi support:
https://github.com/llvm/llvm-project/commit/8674a023bcacb677ce48b8831e2ae35b5aa2d8ef
+ minmax support:
https://github.com/llvm/llvm-project/commit/624973806c5644ccfa84805319b5852edb68d48d