AICS: Simplify VolumeControlInputDescriptor usage

Since we are storing the instance with index [0-NumOfInput], we don't
need to store it in a map.
Using an array
re-write unit test to test smaller behavior
re-write accessor method to unify logging
make use of new defined constant for data check

Bug: 372328699
Flag: com.android.bluetooth.flags.aics_api
Test: m Bluetooth
Change-Id: Id5ddfa65c72ae409be5968b2a60ef629da4ca288