[clang] [clang-tools-extra] [Clang] Implement CWG2813: Class member access with prvalues (PR #95112)

[via cfe-commits]

================
@@ -9182,6 +9182,9 @@ def warn_unused_constructor : Warning<
 def warn_unused_constructor_msg : Warning<
   "ignoring temporary created by a constructor declared with %0 attribute: %1">,
   InGroup<UnusedValue>;
+def warn_discarded_class_member_access : Warning<
+  "left operand of dot in this class member access is discarded and has no effect">,
----------------
Sirraide wrote:

```suggestion
  "discarding left operand of '.' in %select{access to static data member|access to enumerator|call to static member function}0">,
```
(and maybe more cases if I missed any)

https://github.com/llvm/llvm-project/pull/95112