Add on-value-change callback to propstore.

Add on-value-change callback to VehiclePropertyStore. When a new
value is written to propStore or a value is updated, the callback
would be invoked which could be used to inform VHAL client about
value updates.

Test: atest VehicleHalVehicleUtilsTest
Bug: 201830716
Change-Id: I980f5e8c34d9f872f962776859de9615ce3bf690