[docs] Update DebuggingJITedCode page after fix in LLDB

Generalize the documentation to include both, GDB and LLDB. Add a link to the interface
definition. Make a note on MCJIT's restriction to ELF. Mention the regression and bugfix
in LLDB as well as the jit-loader setting for macOS. Update the command line session to
use LLDB instead of GDB.

Reviewed By: lhames

Differential Revision: https://reviews.llvm.org/D90789