Add support for LLDB

I mostly use lldb on mac and gdb on linux. Could this be made to work with lldb as well?

The mapping in commands from gdb to lldb is 1:1, the commands are often just named slightly differently. I'd like to use something that gives me a smooth experience with both.

Start by tracing the existing gdb command mappings and debugger integration; the issue says LLDB commands are often named differently but does not identify files or tests. Done should mean LLDB works alongside gdb, including a smooth macOS experience while preserving the existing Linux workflow.

Written by the indexing model from the issue text.