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

gdb/breakpoint.c

@@ -5491,7 +5491,6 @@ bpstat_stop_status (const address_space *aspace,
 	  if (bs->stop)
 	    {
 	      ++(b->hit_count);
-	      gdb::observers::breakpoint_modified.notify (b);
 
 	      /* We will stop here.  */
 	      if (b->disposition == disp_disable)
@@ -5501,6 +5500,7 @@ bpstat_stop_status (const address_space *aspace,
 		    b->enable_state = bp_disabled;
 		  removed_any = 1;
 		}
+	      gdb::observers::breakpoint_modified.notify (b);
 	      if (b->silent)
 		bs->print = 0;
 	      bs->commands = b->commands;