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.
Before these changes each value of latency were actually 5ms, with a
minimum latency of ~10 ms. If it was set to 4 ms on the UI, the actual
latency was 10 + 5 * 4 = 30 ms.
Now 30 ms on the UI means 30 ms on the backend.
OpenALStream was querying the backend for AL_EXT_float32 support (which
suceeds), but AL_FORMAT_STEREO_FLOAT32 was defined incorrectly.
Also changes OpenALStream to query for AL_EXT_MCFORMATS (multichannel
support) rather than hard-coding that it doesn't work on macOS.
Replaces old and simple usages of std::atomic<bool> with Common::Flag
(which was introduced after the initial usage), so it's clear that
the variable is a flag and because Common::Flag is well tested.
This also replaces the ready logic in WiimoteReal with Common::Event
since it was basically just unnecessarily reimplementing Common::Event.