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

[Aaron Ballman via llvm-commits]

https://github.com/AaronBallman commented:

> I will try to get back on this PR tomorrow though so it doesn't stagnate much longer.

I guess that didn't work out as planned, but I got to it today. :-D

FWIW, this is a case where fuzz testing may help shake out parser issues.

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