[clang-tools-extra] [clangd] Add feature modules registry (PR #153756)

[kadir çetinkaya via cfe-commits]

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@@ -185,6 +194,8 @@ class FeatureModuleSet {
 
 template <typename Mod> int FeatureModuleSet::ID<Mod>::Key;
 
+typedef llvm::Registry<FeatureModule> FeatureModuleRegistry;
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kadircet wrote:

nit: prefer `using X = Y`

https://github.com/llvm/llvm-project/pull/153756