[llvm] [llvm][utils] Add summary formatter for SmallBitVector (PR #150542)

[via llvm-commits]

https://github.com/jimingham approved this pull request.

This can't hurt anything, and if it works in sniff testing is a good sign it's right.
At some point we need to come up with a way of testing the llvm & lldb data formatters but that's obviously a bigger change that's out of scope for this PR.

https://github.com/llvm/llvm-project/pull/150542