[clang-tools-extra] [llvm] [llvm] add support for mustache templating language (PR #105893)

[Nicolas van Kempen via cfe-commits]

https://github.com/nicovank commented:

I like Mustache! Just took a quick look at this following your Discourse post.

Do the custom allocators make any significant performance difference (measure)? Wouldn't want to prematurely optimize. They're the kind of thing that make maintenance annoying and can be hard to remove later.

Same with `SmallString<0>` / `SmallVector`, in some places `std::string` may be sufficient. I think this first implementation can afford to be as simple as possible, specific implementation optimizations can be added later.

Should `Token` and `ASTNode` be present in the `Mustache.h` header at all?

https://github.com/llvm/llvm-project/pull/105893