[lldb] optionally match the `__debug` namespace for libstdc++ containers. (#140727)
If libstdc++ is compiled with `_GLIBCXX_DEBUG` flag it puts the containers in the namespace `std::__debug`. this causes the summary and synthetic formatters not to match the types. The formatters is updated to optionally match the `__debug::`.
The formatters now clashed with the libc++ containers namespace regex which uses `std::__1` namespace
The libc++ formatter is loaded first, then the libstdc++ since the priority of the formatters in lldb is the last one added.
Fixes #60841