This gets rid of a blocking operation, improving performance and fixing
https://bugs.dolphin-emu.org/issues/12893.
This also makes us no longer directly access the state of certain UI
elements from the CPU thread, which probably wasn't thread-safe but
doesn't seem to have caused any observable issues so far.
SPDX standardizes how source code conveys its copyright and licensing
information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX
tags are adopted in many large projects, including things like the Linux
kernel.
As a side effect of 9c5c3c0, Dolphin's frame counter was changed
to run at 60/50 Hz even if the game is running at a lower framerate
such as 30 fps. Since the TAS input turbo button functionality
toggled the state of a button every other frame as reported by
the frame counter, this change made the turbo button functionality
not work with 30/25 fps games.
I believe it would be hard to change the frame counter back to
how it used to work without undermining the point of 9c5c3c0,
and I'm not sure if doing so would be desireable or not anyway,
so what I'm doing instead is letting the user determine how long
turbo button presses should last. This lets users avoid the 30/25
fps game problem while also granting additional flexibility.
Perhaps there is some game where it is useful to mash at a speed
which is slower than frame perfect.
