VCS: Refactor Device Volume API for generic usage

Refactors the Device Volume API to be fully independent of the Group
Volume API, allowing both APIs to coexist without breaking existing logic.

Enhance setDeviceVolume to include mute state control.

Update device volume and mute state in group operations to reflect
any changes in group volume or mute state.

Modify getDeviceVolume to fall back to group volume if device-specific
volume data does not exist (e.g., when a device is newly added to a group).

Modify getGroupVolume to fall back to device volume if group-specific
volume data does not exist (e.g., when group volume has not been set before).

Modify getMute to fall back to group mute state if device-specific
mute state does not exist.

Modify getGroupMute to fall back to device mute state if device-specific
mute state does not exist.

Remove the case for non-autonomous device volume changes from
handleVolumeControlChanged, as no action is required in such scenarios.

Remove group volume restoration in connectionStateChanged#Connected,
as it is already handled in handleVolumeControlChanged.

Bug: 339760224
Bug: 381507732
Test: atest VolumeControlServiceTest
Change-Id: I4ebb08d671025f2ffcce13fc782b56a06a605efe