[lldb/Interpreter] Fix session-save-on-quit when using ^D

Previously, when `interpreter.save-session-on-quit` was enabled, lldb
would save the session transcript only when running the `quit` command.

This patch changes that so the transcripts are saved when the debugger
object is destroyed if the setting is enabled.

rdar://72902650

Differential Revision: https://reviews.llvm.org/D105038



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