[clang-tools-extra] [llvm] Apply modernize-use-starts-ends-with on llvm-project (PR #89140)

[Nicolas van Kempen via llvm-commits]

nicovank wrote:

`std::string::starts_with` is only available from C++20, and LLVM is limited to C++17 as far as I know. However, the two objects here are `StringRef` so this is safe.

https://github.com/llvm/llvm-project/pull/89140