[lldb/crashlog] Refactor CrashLogParser into a Factory pattern

This patch should fix an undefined behaviour that's happening when
parsing a crash report from an IDE. In the previous implementation, the
CrashLogParser base class would use the `__new__` static class method to
create the right parser instance depending on the crash report type.

For some reasons, the derived parser initializer wouldn't be called when
running the command from an IDE, so this patch refactors the
CrashLogParser code to replace the use of the `__new__` method with a
factory `create` static method.

rdar://100527640

Differential Revision: https://reviews.llvm.org/D139951



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