[clang-tools-extra] readability-identifier-naming should add universal default options (PR #171686)

[Victor Chernyakin via cfe-commits]

================
@@ -223,6 +255,31 @@ Options description
 
 A detailed description of each option is presented below:
 
+.. option:: DefaultCase
+
+    When defined, the check will ensure all names by default conform to the
+    selected casing.
+
+.. option:: DefaultPrefix
+
+    When defined, the check will ensure all names by default will add the
+    prefixed with the given value (regardless of casing).
----------------
localspook wrote:

```suggestion
    prefix with the given value (regardless of casing).
```
(looks like the existing option descriptions also have this typo though)

https://github.com/llvm/llvm-project/pull/171686