[lldb] Unify default/hijack listener between Process{Attach,Launch}Info (NFC)

This patch is a simple refactor that unifies the default and hijack
listener methods and attributes between ProcessAttachInfo and
ProcessLaunchInfo.

These 2 classes are both derived from the ProcessInfo base class so this
patch moves the listeners attributes and getter/setter methods to the
base class.

Differential Revision: https://reviews.llvm.org/D148395



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