[clang] [clang-tools-extra] [AstMatcher]`templateArgumentCountIs` support `FunctionDecl` (PR #130416)

[Aaron Ballman via cfe-commits]

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@@ -1090,6 +1090,7 @@ AST_POLYMORPHIC_MATCHER_P2(
 AST_POLYMORPHIC_MATCHER_P(
     templateArgumentCountIs,
     AST_POLYMORPHIC_SUPPORTED_TYPES(ClassTemplateSpecializationDecl,
+                                    VarTemplateSpecializationDecl, FunctionDecl,
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AaronBallman wrote:

It'd probably be good to update the example code above. Also, can you add test coverage to `clang/unittests/ASTMatchers/ASTMatchersNarrowingTest.cpp`?

https://github.com/llvm/llvm-project/pull/130416