Function sixtyfps::testing::mock_elapsed_time

#[no_mangle]
pub extern "C" fn mock_elapsed_time(time_in_ms: u64)

SixtyFPS animations do not use real time, but use a mocked time. Normally, the event loop update the time of the animation using real time, but in tests, it is more convenient to use the fake time. This function will add some milliseconds to the fake time