Report only loaded debug info in statistics dump (#81706)

Currently running `statistics dump` will trigger lldb to load debug info
that's not yet loaded (eg. dwo files). Resulted in a delay in the
command return, which, can be interrupting.

This patch also added a new option `--load-all-debug-info` asking
statistics to dump all possible debug info, which will force loading all
debug info available if not yet loaded.