Add a way to check whether the chest is blocked

[SoSeDiK]

Adds a way to check whether the chest is blocked (due to the block above / a sitting cat).

CraftEnderChest's upper block check is hardcoded, so this PR uses ChestBlock's one instead (they are identical and the implementation makes no sense to change in the future), but if preferred, the check could be extracted into a separated method and used instead.