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

[David Blaikie via cfe-commits]

dwblaikie wrote:

> > Do we care about performance on MSVC ?
> 
> Just responding to this point (although I accept it's moot in the current context): yes we care about performance when building with MSVC - our downstream toolchain is hosted on Windows. I'm sure we're not the only Windows client either.

Do you not bootstrap with clang-cl after building with MSVC? I'd expect that might help at least put you on the same performance tradeoffs as other users, if not be outright better.

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