feat(2d): add start and end signals to Grid node

[ksassnowski]

This PR adds start and end signals to the Grid node. These signals can be used to animate the grid appearing on screen similar to lines or curves work.

Example

export default makeScene2D(function* (view) {
  const grid = createRef<Grid>();

  view.add(
    <Grid
      ref={grid}
      width={'100%'}
      height={'100%'}
      stroke={'#666'}
      start={0.5}
      end={0.5}
    />,
  );

  yield* all(
    grid().end(1, 1).wait(1).to(0.5, 1),
    grid().start(0, 1).wait(1).to(0.5, 1),
  );
});

grid.mp4