[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 stopped halfway, but a performance tip to save copies:
If the constructor or method is going to "own" the data: pass by value and move (some would recommend two overloads, IMO the extra verbosity is not worth the insignificant performance gain).

I wrote [a post](https://nvankempen.com/2022/09/13/cpp-when-to-pass-by-value.html) a while ago if you ever want more background.

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