[lldb] Fix help/pydoc output when the statusline is enabled (#169101)
Using Python's built-in help shows an empty screen when the statusline
is enabled. The issue is the pydoc pager (e.g. less) which doesn't play
nice with the statusline. Use the "plain" pager instead.
I considered making this conditional on the statusline, but to do that
right you would need to register a callback that toggles it every time
the setting changes and that doesn't seem worth the complexity.
Fixes #166610