Rollup merge of #76995 - LingMan:middle_matches, r=varkor

Reduce boilerplate with the matches! macro

Replaces simple bool `match`es of the form

    match $expr {
        $pattern => true
        _ => false
    }

and their inverse with invocations of the matches! macro.

Limited to rustc_middle for now to get my feet wet.

compiler/rustc_middle/src/traits/specialization_graph.rs

@@ -79,10 +79,7 @@ pub enum Node {
 
 impl<'tcx> Node {
     pub fn is_from_trait(&self) -> bool {
-        match *self {
-            Node::Trait(..) => true,
-            _ => false,
-        }
+        matches!(self, Node::Trait(..))
     }
 
     /// Iterate over the items defined directly by the given (impl or trait) node.