Allow partially moved values in match

[cjgillot]

This PR attempts to unify the behaviour between let _ = PLACE, let _: TY = PLACE; and match PLACE { _ => {} }.
The logical conclusion is that the match version should not check for uninitialised places nor check that borrows are still live.

The match PLACE {} case is handled by keeping a FakeRead in the unreachable fallback case to verify that PLACE has a legal value.

Schematically, match PLACE { arms } in surface rust becomes in MIR:

PlaceMention(PLACE)
match PLACE {
  // Decision tree for the explicit arms
  arms,
  // An extra fallback arm
  _ => {
    FakeRead(ForMatchedPlace, PLACE);
    unreachable
  }
}

match *borrow { _ => {} } continues to check that *borrow is live, but does not read the value.
match *borrow {} both checks that *borrow is live, and fake-reads the value.

Continuation of #102256 #104844

Fixes #99180 #53114