[clang] [PAC][clang] Define `PointerAuthQualifier` and `PointerAuthenticationMode` (PR #84384)

[Aaron Ballman via cfe-commits]

================
@@ -2196,6 +2196,16 @@ class ASTContext : public RefCountedBase<ASTContext> {
     return getQualifiedType(type.getUnqualifiedType(), Qs);
   }
 
+  /// \brief Return a type with the given __ptrauth qualifier.
+  QualType getPointerAuthType(QualType Ty, PointerAuthQualifier PointerAuth) {
+    assert(!Ty.getPointerAuth());
+    assert(PointerAuth);
+
+    Qualifiers qs;
+    qs.setPointerAuth(PointerAuth);
+    return getQualifiedType(Ty, qs);
----------------
AaronBallman wrote:

```suggestion
    Qualifiers QS;
    QS.setPointerAuth(PointerAuth);
    return getQualifiedType(Ty, QS);
```
Naming style nits.

https://github.com/llvm/llvm-project/pull/84384