Refactor adjust channels buffer provider.

Combine adjust channels buffer provider and adjust channels non-destructive
buffer provider.
When contracting mono + haptic channels to mono, do not use
adjust_channels to avoid mixing haptic channel into audio channel.

Bug: 125915810
Test: play audio-haptic coupled files
Change-Id: I39916a3e0628a44ed4a148c265564af7135a2176