[clang-tools-extra] [clang-tidy] Fix `modernize-use-constraints` crash on uses of nonstandard `enable_if`s (PR #152938)

[Victor Chernyakin via cfe-commits]

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@@ -78,6 +79,15 @@ matchEnableIfSpecializationImplTypename(TypeLoc TheType) {
     if (!TD || TD->getName() != "enable_if")
       return std::nullopt;
 
+    const TemplateParameterList *Params = TD->getTemplateParameters();
+    if (Params->size() != 2)
+      return std::nullopt;
----------------
localspook wrote:

It looks like specializations of different kinds are represented in the AST as: 
- `FunctionDecl`
- `VarTemplatePartialSpecializationDecl`
- `VarTemplateSpecializationDecl`
- `ClassTemplatePartialSpecializationDecl`
- `ClassTemplateSpecializationDecl`

None of those are subclasses of `TemplateDecl`. That means they wouldn't get past the `getAsTemplateDecl()` check above, so I'm hesitantly removing this check.

https://godbolt.org/z/PqeMe3fsx

https://github.com/llvm/llvm-project/pull/152938