[clang] [clang-tools-extra] Remove `StringLiteral` in favor of `StringRef` (PR #122366)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> > Anyway, my main point was that there are people who care about performance on Windows, so please don't treat it as a second-class citizen.
> 
> Yeah, I don't want to treat folks on Windows as second class citizens by any means - but I wouldn't mind/hope we can treat folks who care about performance but don't build their performance-critical binaries with clang, on platforms clang supports, as a lower priority.

Consider testing as a counter example. We don't seriously expect anyone to do a bootstrap build each time they want to run their tests and folks do still run tests locally on their machine, and may run those tests frequently.

https://github.com/llvm/llvm-project/pull/122366