Notify observer of breakpoint auto-disabling

Notify observer of breakpoint auto-disabling

As breakpoint_modified observer is currently notified upon breakpoint stop
before handling auto-disabling when enable count is reached, the observer
is never notified of the disabling.

The problem affects:
- The MI interpreter enabled= value when reporting =breakpoint-modified
- A Python event handler for breakpoint_modified using the "enabled"
  member of its parameter
- insight: breakpoint GUI window is not properly updated upon auto-disable

This patch moves the observer notification after the auto-disabling
code and implements corresponding tests for the MI and Python cases.

Fixes https://sourceware.org/bugzilla/show_bug.cgi?id=23336

Change-Id: I0c50df4789334071e5390cb46b3ca0d4a7f83c61