Refactor mixCriteria in AudioPolicyMix.

- use std::vector instead of android::Vector
- remove const qualifiers on setters (incorrect by definition)
- remove mutable specifier on mCriteria
- fix assignment to const pointer when actually changing the AudioMix

Bug: 233910083
Test: atest AudioServiceHostTest AudioHostTest AudioPolicyHostTest
Test: Refactoring cl, existing tests pass.
Change-Id: I140c41acbea0f5b88d71587d7633db4e7ceee847