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

[Baranov Victor via cfe-commits]

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@@ -223,6 +226,60 @@ Options description
 
 A detailed description of each option is presented below:
 
+.. option:: DefaultCase
+
+    When defined, the check will ensure all name by default conform to the
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vbvictor wrote:

```suggestion
    When defined, the check will ensure all names by default conform to the
```

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