[lldb/crashlog] Fix sticky image parsing logic

Prior to this patch, when a user loaded multiple crash report in lldb,
they could get in a situation where all the targets would keep the same
architecture and executable path as the first one that we've created.

The reason behind this was that even if we created a new CrashLog
object, which is derived from a Symbolicator class that has a newly
constructoted image list as a default argument, because that default
argument is only created once when the function is defined, every CrashLog
object would share the same list.

That will cause use to append newly parsed  images to the same
Symbolicator image list accross multiple CrashLog objects.

To address this, this patch changes the default argument value for the
image parameter to `None` and only initialize it as an empty list when
no argument was passed.

This also removes the image list stored in each CrashLog parsers since
they shouldn't have any state and should be re-usable. So now, the only
source of truth is stored in the CrashLog object.

rdar://84984949

Differential Revision: https://reviews.llvm.org/D157044



Signed-off-by: Med Ismail Bennani <ismail@bennani.ma>