Migrate utf8_range dependency to a git subtree (#11608)

This will make the CMake workflow easier, where users won't need to either install utf8_range or initialize our submodules.  Since this is a relatively small library that's owned by us, we can just bundle it with protobuf as a subtree

Closes #11608

COPYBARA_INTEGRATE_REVIEW=https://github.com/protocolbuffers/protobuf/pull/11608 from mkruskal-google:utf8_range_dep 57d5d91b
PiperOrigin-RevId: 503314822