[lldb/crashlog] Refactor the CrashLogParser logic

This patch changes the CrashLogParser class to be both the base class
and a Factory for the JSONCrashLogParser & TextCrashLogParser.

That should help remove some code duplication and ensure both class
have a parse method.

Differential Revision: https://reviews.llvm.org/D131085



Signed-off-by: Med Ismail Bennani <medismail.bennani@gmail.com>