[llvm] [LLVM][ADT] Add some more `starts_with`, `ends_with`, and `contains` overloads to `SmallString` (PR #182692)

[Jakub Kuderski via llvm-commits]

https://github.com/kuhar commented:

Looks good but please add some simple unit tests

https://github.com/llvm/llvm-project/pull/182692