Exports API to allow RULE_MATCH_UID support both RECORDERS and PLAYERS mix type

Removes @hide to export AudioMixingRule#Builder#setTargetMixType(), AudioMix#MIX_TYPE_PLAYERS and AudioMix#MIX_TYPE_RECORDERS.

Bug: 183693610
Test: atest com.google.android.gts.audioservice.AudioServiceHostTest
CTS-Coverage-Bug: 191716676
Change-Id: I8eebfc8c139b0bd3ef277863eb46d2c3383eb65e