We were registering the hotplug callback when starting the thread, but
deregistering it when shutting down GCAdapter as a whole. Because the
thread can start and stop potentially many times before GCAdapter shuts
down, this led to callbacks being registered when we already have
callbacks. On Android, this was making Dolphin's Kotlin code for
registering the callback throw an IllegalStateException.

To fix this, deregister the callback when stopping the thread.

Make `s_is_adapter_wanted` and the elements of `s_config_rumble_enabled`
atomic.

The CPU thread reads `s_is_adapter_wanted` and `s_config_rumble_enabled`
in `Output`, while the host thread writes to them in `RefreshConfig`.

The simplest way to trigger this race is to close the `Settings` window
while playing a game with the adapter active.

GCAdapter: Automatically start and stop thread

This keeps the logic encapsulated inside GCAdapter.cpp so callers don't
have to think about it.

Accomplished using `run-clang-tidy` with `performance-move-const-arg,performance-unnecessary-value-param,modernize-pass-by-value`.

Changed arguments to const references, removed them where inappropriate (e.g. sink parameters). Same with std::move.

Manually reviewed each change to make sure that it makes sense, and do something more appropriate if possible.

Yellow squiggly lines begone!
Done automatically on .cpp files through `run-clang-tidy`, with manual corrections to the mistakes.
If an import is directly used, but is technically unnecessary since it's recursively imported by something else, it is *not* removed.
The tool doesn't touch .h files, so I did some of them by hand while fixing errors due to old recursive imports.
Not everything is removed, but the cleanup should be substantial enough.
Because this done on Linux, code that isn't used on it is mostly untouched.
(Hopefully no open PR is depending on these imports...)