audio_server: Unify audio_patch creation

Provide PatchBuilder helper class instead of fiddling with
struct audio_patch directly.

Rename 'getAudioPortConfig' methods of AudioFlinger helper
classes into 'toAudioPortConfig' to match classes
of AudioPolicyManager.

Factor out common code in AudioPolicyManager that was
adding audio patches. For that, AudioOutputDescriptor now inherits
from AudioSessionInfoProvider, and the latter has been extended
with 'setPatchHandle' method.

Test: switch to/from Bluetooth on phone calls and media playback,
      use camcorder
Change-Id: Idd99645dc6943ed078c4d94d0197fead7831ab4d