[clang] Add Clang attribute to ensure that fields are initialized explicitly (PR #102040)

[via cfe-commits]

================
@@ -1419,6 +1419,35 @@ is not specified.
   }];
 }
 
+def ExplicitInitDocs : Documentation {
----------------
higher-performance wrote:

Sure, please see update.

https://github.com/llvm/llvm-project/pull/102040