Signed-off-by: Steven Noonan <steven@uplinklabs.net>

We already map the in:out 1:1 mappings above the switch statement, but
the code for "simple" mapping stomps on the mappings.

Also, even before that loop was added, mix mode "simple" did not
necessarily map to the same channel types you'd expect. For example, if
you have a 6-channel input and 8-channel output, you would get something
like this with "simple":

  Correct:  CHANNEL_FRONT_LEFT -> CHANNEL_FRONT_LEFT
  Correct:  CHANNEL_FRONT_RIGHT -> CHANNEL_FRONT_RIGHT
  Correct:  CHANNEL_FRONT_CENTER -> CHANNEL_FRONT_CENTER
  Correct:  CHANNEL_LFE -> CHANNEL_LFE
  Wrong:    CHANNEL_SIDE_LEFT -> CHANNEL_BACK_LEFT
  Wrong:    CHANNEL_SIDE_RIGHT -> CHANNEL_BACK_RIGHT

Instead of just assuming the input channel map is a truncation of the
output channel map and has channels in the same order, just keep the
existing 1:1 mappings and hope that's sufficient.
Signed-off-by: Steven Noonan <steven@uplinklabs.net>

This is disabled by default for backwards compatibility. Use the
`calculateLFEFromSpatialChannels` config option to enable this.

If the LFE channel exists in the output channel map but not the input
channel map, we would previously just give it a weight of 0, which
caused it to not be filled.

This gives LFE a weight of 1.0f/$NumberOfSpatialChannels and basically
makes it omnidirectional.
Signed-off-by: Steven Noonan <steven@uplinklabs.net>

The error here is that exactly-matching channels were not having a
weight calculated which resulted in them being silenced.

Public issue https://github.com/mackron/miniaudio/issues/480

 Cast from 'void*' to pointer to non-'void' requires explicit type cast error under msvc compiler

Public issue https://github.com/mackron/miniaudio/issues/500

Public issue https://github.com/mackron/miniaudio/issues/499

Public issue https://github.com/mackron/miniaudio/issues/493

Public issue https://github.com/mackron/miniaudio/issues/494

Public issue https://github.com/mackron/miniaudio/issues/482

Public issue https://github.com/mackron/miniaudio/issues/485

Pubic issue https://github.com/mackron/miniaudio/issues/469