[clang] [llvm] [lld] [lldb] [clang-tools-extra] [ADT] Rename SmallString::{starts,ends}with to {starts,ends}_with (PR #74916)

[Kazu Hirata via cfe-commits]

kazutakahirata wrote:

> flang and bolt are not changed?

Right.  Somehow, `SmallString<N>::{startswith,endswith}` do not occur there.  By the way, they are not to be confused with `StringRef::{startswith,endswith}, which is everywhere.

https://github.com/llvm/llvm-project/pull/74916