[Demangle][Rust] Parse trait definitions

Part of https://reviews.llvm.org/D102549

Author: tmiasko

llvm/lib/Demangle/RustDemangle.cpp

@@ -162,6 +162,14 @@ void Demangler::demanglePath() {
     print(">");
     break;
   }
+  case 'Y': {
+    print("<");
+    demangleType();
+    print(" as ");
+    demanglePath();
+    print(">");
+    break;
+  }
   case 'N': {
     char NS = consume();
     if (!isLower(NS) && !isUpper(NS)) {

llvm/test/Demangle/rust.test

@@ -49,6 +49,11 @@ CHECK: <_ as Clone>
 CHECK: <_ as Clone>
        _RXs_C5cratepC5Clone
 
+; Trait definition
+
+CHECK: <_ as Ord>
+       _RYpC3Ord
+
 ; Generic type arguments
 
 CHECK: generic::<_>