[clang-tools-extra] [clang-tidy] Add AllowExplicitReferencedInitialValues to `readability-enum-initial-value` (PR #189459)

[Björn Svensson via cfe-commits]

================
@@ -92,3 +92,20 @@ Options
       g0 = 1, // Not allowed if AllowExplicitSequentialInitialValues is false.
       g1 = 2,
       g2 = 3,
+    };
+
+.. option:: AllowExplicitReferencedInitialValues
----------------
bjosv wrote:

Sound Ok, updated to `AllowReferencedInitialValues`.
An alternative could be `AllowSelfReferencedInitialValues`

https://github.com/llvm/llvm-project/pull/189459