[audio] Add playback hardening override plumbing

Allows for AudioService to communicate that playback hardening has been
enabled via override by API, which results in skipping the flag checking
and exemption logic within audioserver.

Misc plumbing to get that bit of data available at the track level.

Bug: 376481063
Test: manual verification via adb shell set-hardening
Flag: EXEMPT test only
Change-Id: I75bd475d1fe0c415204ebda71c29043eb079ddf7