Public issue https://github.com/mackron/miniaudio/issues/836.

This adds the following flags:

  * MA_SOUND_FLAG_LOOPING
  * MA_RESOURCE_MANAGER_DATA_SOURCE_FLAG_LOOPING

These can be used to initialize sounds and resource managed data
sources to loop by default. This is the recommended way to enable
looping for streams. The `isLooping` config option in
`ma_sound_config` and `ma_resource_manager_data_source_config` has been
deprecated. If you are using those, you should switch to the new flag
or else you'll get compiler errors when upgrading to a future version.

Public issue https://github.com/mackron/miniaudio/issues/811

When processing a node, miniaudio will read into a temporary buffer
before mixing input attachments. This commit removes the per-node heap
allocation and replaces it with a per-graph stack. This should result
in less memory usage at larger scales, but at the expense of slightly
more usage at smaller scales.

The size of the stack can be configured via ma_node_graph_config. If
ma_engine is being used, it can be done via ma_engine_config.

Previously, processing a node would involve a temporary buffer
allocated on the stack. Because this was fixed size, it would result in
processing being sub-divided into chunks in order to avoid overflowing
that buffer. This becomes an issue when a node needs to have a known
processing size. An example might be some kind of effect that requires
processing be in powers of two.

With this commit, the `processingSizeInFrames` variable in
`ma_node_graph_config` can be used to make it so processing always
happens in fixed sized chunks. In this situations, it's recommended you
always call `ma_node_graph_read_pcm_frames()` with a frame count of a
multiple of `processingSizeInFrames`.

The allocation strategy used here is not optimal and will be improved
in future commits. It currently allocates a buffer per-node, but since
the data contained within it is transient in nature, it should be
possible to use a global fixed sized stack that supports allocating a
variable amount of space within the stack buffer.

Public issue https://github.com/mackron/miniaudio/issues/810

Public issue https://github.com/mackron/miniaudio/issues/805

Public issue https://github.com/mackron/miniaudio/discussions/800

Public issue https://github.com/mackron/miniaudio/issues/779

Use the MA_PTHREAD_REALTTIME_THREAD_PRIORITY define.

This is useful because MA_ASSERT is only defined in the implementation
section of miniaudio.h which can cause issues when people copy/paste
the code and use it in a file that does not have visibility of the
implementation.

Note that there are still more references to implementation-defined
macros, but these have been moved to the public section in the dev-0.12
branch so I'm not bothering to change those just yet.

Public issue https://github.com/mackron/miniaudio/issues/787

Use `#define MA_AAUDIO_MIN_ANDROID_SDK_VERSION 26` if you need to
support SDK version 26.

Define MA_AAUDIO_MIN_ANDROID_SDK_VERSION to specify the minimum
required SDK version for enabling the AAudio backend.

Public issue https://github.com/mackron/miniaudio/issues/781