Adjust places where profiling callbacks invoked (to match Mono GC)

Adjust places where profiling callbacks invoked (to match Mono GC)

* alloc.c (GC_try_to_collect_inner): Move sending of GC_EVENT_START to
the beginning of function (i.e. send right after GC_dont_gc check);
move sending of GC_EVENT_END from GC_finish_collection to the end of
this function (send it only if collection completed successfully); add
TODO note about GC_EVENT_ABANDON notification.
* alloc.c (start_world_inner): Remove.
* alloc.c (GC_stopped_mark): Send GC_EVENT_PRE_STOP_WORLD,
GC_EVENT_POST_STOP_WORLD, GC_EVENT_PRE_START_WORLD,
GC_EVENT_POST_START_WORLD only if THREADS.
* alloc.c (GC_stopped_mark): Send GC_EVENT_MARK_START before
minimizing junk left in registers/stack (instead of after).
* alloc.c (GC_stopped_mark): Do not send GC_EVENT_MARK_END in case of
abandoned collection (add TODO note about GC_EVENT_MARK_ABANDON).
* alloc.c (GC_stopped_mark): Send GC_EVENT_MARK_END after checking
debugged objects for consistency (instead of before it).
* darwin_stop_world.c (GC_suspend_thread_list): Send
GC_EVENT_THREAD_SUSPENDED (in addition to that in GC_stop_world).
* darwin_stop_world.c (GC_thread_resume): Move sending of
GC_EVENT_THREAD_UNSUSPENDED from GC_start_world().
* pthread_stop_world.c (GC_suspend_all, GC_start_world): Do not send
GC_EVENT_THREAD_SUSPENDED if pthread_kill/android_thread_kill failed.
* pthread_stop_world.c (GC_start_world): Send
GC_EVENT_THREAD_UNSUSPENDED after pthread_resume_np (in case of
GC_OPENBSD_UTHREADS).
* win32_threads.c (GC_stop_world): Move sending of
GC_EVENT_THREAD_SUSPENDED to GC_suspend().
* win32_threads.c (GC_suspend, GC_start_world): Remove redundant cast
to void* of THREAD_HANDLE().