This addresses a bit of thread unsafety mentioned in a comment, and
fixes a 'ScheduleEvent_Threadsafe from main thread' message.
To make this work nicely, make PauseAndLock call DeclareAsCPUThread -
i.e. while you have the CPU thread locked, you can consider yourself the
CPU thread.
Replaces them with forward declarations of used types, or removes them entirely if they aren't used at all. This also replaces certain Common headers with less inclusive ones (in terms of definitions they pull in).
Core::Shutdown was only called on app exit, yet the emu thread exits
whenever emulation stops; if you launched a new game it would just join
via the destructor when s_emu_thread was set to a new thread.
(Incidentally, the destructor also makes explicitly joining on app exit
rather pointless.)
Because the GUI thread wasn't waiting for the CPU thread to fully shut
down, Core::IsRunning would remain true briefly after CFrame::DoStop
which, given Dolphin's penchant for accessing variables belonging to
other threads, can only mean trouble... In my case, because the previous
commit caused UpdateGUI, which is called at the end of DoStop, to call
PauseAndLock, which checks IsRunning, pressing stop at the right time
would cause strange behavior.
It now affects the GPU determinism mode as well as some miscellaneous
things that were calling IsNetPlayRunning. Probably incomplete.
Notably, this can change while paused, if the user starts recording a
movie. The movie code appears to have been missing locking between
setting g_playMode and doing other things, which probably had a small
chance of causing crashes or even desynced movies; fix that with
PauseAndLock.
The next commit will add a hidden config variable to override GPU
determinism mode.
