[llvm] [ADT] Add `[[clang::lifetimebound]]` annotations to Twine.h (PR #210474)

[Oliver Stöneberg via llvm-commits]

firewave wrote:

Obviously these annotations should exist but it appears they were added based manual review but there's compiler warnings for them which provide suggestions. I think this should be a tool-driven change to make sure the existing functionality works/is complete.

And also it would only report lifetime issues if the appropriate warnings are enabled in the builds. Is that the case? (I am not of the loop on this, so sorry is this turned out to be rather rhetorical).

https://github.com/llvm/llvm-project/pull/210474