[clang] [clang][Sema] Subclass `-Wshorten-64-to-32` under `-Wimplicit-int-conversion` (PR #80814)

[Aaron Ballman via cfe-commits]

================
@@ -149,7 +149,12 @@ Improvements to Clang's diagnostics
   prints.
 
 - Clang now diagnoses member template declarations with multiple declarators.
-- Clang now diagnoses use of the ``template`` keyword after declarative nested name specifiers.
+
+- Clang now diagnoses use of the ``template`` keyword after declarative nested
+  name specifiers.
+
+- Added `-Wshorten-64-to-32` diagnostics to enable when
+  `-Wimplicit-int-conversion` is enabled.
----------------
AaronBallman wrote:

```suggestion
- The ``-Wshorten-64-to-32`` diagnostic is now grouped under ``-Wimplicit-int-conversion`` instead
   of ``-Wconversion``. Fixes `#69444 <https://github.com/llvm/llvm-project/issues/69444>`_.
```

https://github.com/llvm/llvm-project/pull/80814