Implemented SWITCH_USER in the emulated User HAL.

Examples:

$ adb shell lshal debug android.hardware.automotive.vehicle@2.0::IVehicle/default --user-hal
No InitialUserInfo response
No SwitchUser response

$ adb shell lshal debug android.hardware.automotive.vehicle@2.0::IVehicle/default --set 299896584 a 1 i 666 i 3 i 1 s "D\\'OH!"
Set property {.timestamp = 63698971001637, .areaId = 1, .prop = 299896584, .status = AVAILABLE, .value = {.int32Values = [3]{666, 3, 1}, .floatValues = [0]{}, .int64Values = [0]{}, .bytes = [0]{}, .stringValue = "D'OH!"}}

$ adb shell lshal debug android.hardware.automotive.vehicle@2.0::IVehicle/default --user-hal
No InitialUserInfo response
SwitchUser response: {.timestamp = 63698971001637, .areaId = 1, .prop = 299896584, .status = AVAILABLE, .value = {.int32Values = [3]{666, 3, 1}, .floatValues = [0]{}, .int64Values = [0]{}, .bytes = [0]{}, .stringValue = "D'OH!"}}

Test: see commands above
Bug: 150409110

Change-Id: Id5b92774fccebbc39ed8d3f553df3f5aa30fc656