For anyone stumbling on this in the future, this work was RFC’d in [RFC] Adding Register Field Information to lldb-server and as of [llvm][lldb][Docs] Add release note for register field info in lldb-s… · llvm/llvm-project@c4e57b1 · GitHub is complete and will be in LLDB 18.
Meaning that there is no need to use gdbserver to get field information (though of course we are compatible with it still). lldb-server handles it all now.