Expand /worldborder get with additional subcommands

Currently, /worldborder get only returns the current worldborder size, even though the worldborder stores several other properties internally.

It would be very useful if the command supported additional subcommands to query all existing worldborder values, especially for datapacks, mapmaking, automation, debbuging and command consistency.

Suggested syntax :

/worldborder get size

/worldborder get center x
/worldborder get center z

/worldborder get damage amount
/worldborder get damage buffer

/worldborder get warning distance
/worldborder get warning time

This would make the /worldborder command much more consistent with other modern commands and would allow creators to retrieve world border data using execute store.

Example :

execute store result score #center_x data run worldborder get center x

Currently, creators must manually calculate or track these values externally, even though the game already knows them internally.

This change would improve command usability without changing existing functionality.