Structure Block Tools

Added function sbtools:shrink_box_to_fit: Decreases the size of the selected Structure Block's Bounding Box until the contained structure is perfectly fitted.

• The box will stop shrinking when it encounters any block NOT listed in #sbtools:ignore_when_shrinking, which by default contains air, water, lava, and structure voids.
• For very large bounding boxes, you may need to increase the value of the max_command_sequence_length gamerule in order for this function to work properly. (There are a ton of commands running, but each one is very lightweight, so overall this function is still less laggy than Dynamic Fill)
• This function will not increase the size of the bounding box, and I currently have no plans to implement such functionality.

Added version compatibility going back to Minecraft 1.21, via the use of an Overlay. (There was only 1 function preventing this compatibility, making the overlay trivial to implement.)