[lldb][docs] Cleanup the Python doc strings for SB API classes

[lldb][docs] Cleanup the Python doc strings for SB API classes

The first line of the doc string ends up on the SB API class summary at
the root page of the Python API  web page of LLDB. Currently many of the
descriptions are missing or are several lines which makes the table really
hard to read.

This just adds the missing docstrings where possible and fixes the formatting
where necessary.