Similar to commits 1686f4e8 and
30a5dd26

This allows canceling the blocking method LockWaitWriteAvailable(),
and thus allows breaking free of misbehaving ALSA drivers, avoiding a
MPD lockup.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/966

"DEFAULT" is a bad name - all it says is that it's the default value,
but it doesn't say what it means.  The name NOTICE mimics the syslog
level.

Our AudioObjectGetPropertyDataT() wrapper throws exception on error,
and calling it from OSXOutput::Disable() can cause MPD crash due to
std::terminate().

Closes https://github.com/MusicPlayerDaemon/MPD/issues/932

According to https://developer.android.com/ndk/guides/audio/opensl/android-extensions

This feature was mentioned in https://github.com/MusicPlayerDaemon/MPD/issues/922

Wait until there is data in the ring buffer.

Wait until there is some data; don't let our render callback be
invoked without any data.

We shouldn't restart the AudioUnit while the ring buffer is empty, or
else our render callback may emit noise.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/771

This will keep track of AudioOutputUnitStart() and
AudioOutputUnitStop().  This will provide some separation between "not
(yet) (re)started" and "paused".

This shall be done by Close(), which will be called automatically
after an error.

Move build rules from src/output/plugins/meson.build

The formula in osx_output_score_sample_rate() to detect multiples of
the source sample rate was broken: when given a 44.1 kHz input file,
it preferred 16 kHz over 48 kHz, because its `frac_portion(16)=0.75`
is smaller than `frac_portion(48)=0.91`.

That formula, introduced by commit 40a1ebee, looks completely
wrong.  It doesn't do what the code comment pretends it does.

Instead of using that `frac_portion` to calculate a score, this patch
adds to the score only if `frac_portion` is nearly `0` or `1`.  This
means that the factor is nearly integer.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/904