[clang] [Clang] update reasoned delete diagnostic kind to use Extension, making it pedantic only (PR #114713)

[Aaron Ballman via cfe-commits]

================
@@ -464,6 +464,8 @@ Improvements to Clang's diagnostics
 
 - Clang now diagnoses ``[[deprecated]]`` attribute usage on local variables (#GH90073).
 
+- Clang now diagnoses misused reasoned ``delete("reason")`` warnings only in pedantic mode. (#GH109311).
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AaronBallman wrote:

```suggestion
- Clang now diagnoses ``= delete("reason")`` extension warnings only in pedantic mode rather than on by default. (#GH109311).
```

https://github.com/llvm/llvm-project/pull/114713