Add the stop spectating entity rule type

[haykam821]

This pull request implements a rule type for players stopping spectating entities, which is useful for restricting the player's actions when the game is controlling the camera.

To use this rule, games can deny it when provided a GameActivity instance:

gameSpace.setActivity(activity -> {
            activity.deny(GameRuleType.STOP_SPECTATING_ENTITY);

            // Other game setup
            // ...
});