VolumeControl: Fix restoring earbuds volume

If we stream to one earbud and the second earbud connects with a
different volume level and a flag saying that it is a User-set volume is
set, we should realign its volume to the existing stream volume that was
probably already adjusted to the users liking.

We should apply this new volume to the system only if this is the first
earbud that has connected.

To make sure there is no race between connection and volume state change
events, we need to pass the volume event via the state machine just like
the connection event is. Otherwise the order of events arrival in the
service may differ from the order they were sent.

Bug: 373377157
Test: atest GoogleBluetoothInstrumentationTests
Flag: EXEMPT; Regression covered with unit test
Change-Id: Ifec0ae193a32019e091380dcc7b23f5fe097211f