Use StringRef::{starts,ends}_with (NFC)

This patch replaces uses of StringRef::{starts,ends}with with
StringRef::{starts,ends}_with for consistency with
std::{string,string_view}::{starts,ends}_with in C++20.

I'm planning to deprecate and eventually remove
StringRef::{starts,ends}with.
GitOrigin-RevId: b8f89b84bc26c46a5a10d01eb5414fbde3c8700a
2 files changed