Bump regalloc2 to 0.5.0 (#5345)

* Bump the regalloc2 dependency to 0.5.0
* Replace preg_set_from_machine_env with PRegSet::from
* Vet the regalloc2 update

winch/codegen/Cargo.toml

@@ -17,7 +17,7 @@ target-lexicon = { workspace = true, features = ["std"] }
 # In the next iteration we'll factor out the common bits so that they can be consumed
 # by Cranelift and Winch.
 cranelift-codegen = { workspace = true }
-regalloc2 = "0.4.2"
+regalloc2 = "0.5.0"
 
 [features]
 x64 = ["cranelift-codegen/x86"]