[clang] [Clang][UnsafeBufferUsage] Warn about two-arg string_view constructors. (PR #180471)

[Prajwal P J via cfe-commits]

pjalwadi wrote:

@rohanjr, Thanks for the feedback. I chose to isolate the string_view logic into a separate validator to prevent regressions in the std::span analysis. This ensures that the stricter safety rules for mutable buffers remain untouched while allowing more flexible patterns for read-only views

https://github.com/llvm/llvm-project/pull/180471