[clang-tools-extra] [clangd] Make EnableFunctionArgSnippets option string-typed (PR #121178)

[Haojian Wu via cfe-commits]

================
@@ -242,13 +242,13 @@ opt<std::string> FallbackStyle{
     init(clang::format::DefaultFallbackStyle),
 };
 
-opt<int> EnableFunctionArgSnippets{
+opt<std::string> EnableFunctionArgSnippets{
----------------
hokein wrote:

We could also consider the following option, but up to you.
```
enum FunctionArgSnippetsFlag { True, False, None, ... };
opt<FunctionArgSnippetsFlag> EnableFunctionArgSnippets{...
  values(
    clEnumValN(FunctionArgSnippetsFlag::True, "true", ...),
    clEnumValN(FunctionArgSnippetsFlag::True, "True", ...),
    ...
  ),
};
  
```

https://github.com/llvm/llvm-project/pull/121178