[GlobalISel] Add `combine` action for C++ combine rules (#135941)

Adds a `combine` action (DAG operator) which allows for easy definition of
combine rule that only match one or more instructions, and defer all remaining
match/apply logic to C++ code.

This avoids the need for split match/apply function in such cases. One function
can do the trick as long as it returns `true` if it changed any code.

This is implemented as syntactic sugar over match/apply. The combine rule is
just a match pattern BUT every C++ pattern inside is treated as an "apply" function.
This makes it fit seamlessly with the current backend.

Fixes #92410

0 files changed, 0 insertions, 0 deletions