func (f *Field) RotatePieceLeft(piece *Piece, x, y int, angle Angle) Angle {
	if piece.collides(f, x, y, angle.RotateLeft()) {
		return angle
	}
	return angle.RotateLeft()
}
func (f *Field) RotatePieceLeft(piece *Piece, x, y int, angle Angle) Angle {
	if piece.collides(f, x, y, angle.RotateLeft()) {
		return angle
	}
	return angle.RotateLeft()
}
// RotatePieceLeft tries to rotate the piece to the left
// and returns the piece's next angle.