This makes devices and decoders more robust when the resampler does not
support retrieval of required input frame counts from a given output
frame count, which can happen with custom resamplers.

This changes ma_resampler_get_required_input_frame_count() and
ma_resampler_get_expected_output_frame_count() to return a result code
so that MA_NOT_IMPLEMENTED can be checked and an alternative code path
can be run for dealing with caching of data.

This removes the dependency on the ma_resampler object.

Public issue https://github.com/mackron/miniaudio/issues/162

Public issue https://github.com/mackron/miniaudio/issues/340

Fix invalid vsnprintf buffer size

Was performing a `sizeof` on a pointer, which causes a warning to be
generated.

This adds a capacity parameter for added safety. It also changes the
order of parameters to make it a bit more consistent.

This commit also removes the onGetChannelMap callback from the decoding
backend vtable.

Allocation callbacks must now implement onRealloc() themselves. This is
no longer emulated by miniaudio.

With this change, ma_decoder should now be fully consistent with other
data sources.

This makes ma_decoder_read_pcm_frames() consistent with other data
sources. It now returns a result code and outputs the number of frames
read via an output parameter.

This is now consistent with all other data sources:

  * Returns a result code
  * Length is returned via an output parameter

Use the `encodingFormat` variable in the config instead.

This also renames the `resourceFormat` variables used by the encoder to
`encodingFormat`.