Use constants when Bt flag is not enabled

Using the exported Bt flag supported_metadata_device_types_apis to
determine whether to use the BtDevice constants. We are duplicating the
constants for clients that have written values with the given metadata
keys (see FastPair initial implementation)

Flag: com.android.bluetooth.flags.Flags.supportMetadataDeviceTypesApis
Test: manual device type change
Bug: 335936458
Change-Id: I582e12967bbc4787d278964beb7a450518bc93f9