Update worldedit-sponge to API 8

[octylFractal]

This replaces #1289 and updates to the current tip, along with incorporating #1766 for a better lifecycle. It's currently non-functional due to what I presume is Sponge bugs, but once it's all ironed out and confirmed to be working, it'll become ready for review! Feel free to take a look now.

• Fix completions
• Re-add bStats (Add support for Sponge API 8 Bastian/bstats-metrics#97)
• Investigate VALIDATION side effect

[codecov]

Codecov Report

Merging #1771 (ac8ac86) into version/7.2.x (ab61a84) will decrease coverage by 0.11%.
The diff coverage is 0.00%.

@@                 Coverage Diff                 @@
##             version/7.2.x    #1771      +/-   ##
===================================================
- Coverage            10.77%   10.66%   -0.12%     
  Complexity            1090     1090              
===================================================
  Files                  824      831       +7     
  Lines                37914    38320     +406     
  Branches              4318     4371      +53     
===================================================
  Hits                  4085     4085              
- Misses               33634    34040     +406     
  Partials               195      195              

Impacted Files	Coverage Δ
.../com/sk89q/worldedit/sponge/CUIChannelHandler.java	0.00% <0.00%> (ø)
...ava/com/sk89q/worldedit/sponge/CommandAdapter.java	0.00% <0.00%> (ø)
...ain/java/com/sk89q/worldedit/sponge/Constants.java	0.00% <0.00%> (ø)
...java/com/sk89q/worldedit/sponge/SpongeAdapter.java	0.00% <0.00%> (ø)
...om/sk89q/worldedit/sponge/SpongeBiomeRegistry.java	0.00% <0.00%> (ø)
.../worldedit/sponge/SpongeBlockCategoryRegistry.java	0.00% <0.00%> (ø)
...om/sk89q/worldedit/sponge/SpongeBlockMaterial.java	0.00% <0.00%> (ø)
...om/sk89q/worldedit/sponge/SpongeBlockRegistry.java	0.00% <0.00%> (ø)
...om/sk89q/worldedit/sponge/SpongeCommandSender.java	0.00% <0.00%> (ø)
.../java/com/sk89q/worldedit/sponge/SpongeEntity.java	0.00% <0.00%> (ø)
... and 21 more

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[me4502]

Partially blocked by SpongePowered/Sponge#3585 (Unsure if acceptable to merge before this is fixed) Resolved by Sponge

[me4502]

From my look-overs and testing this appears to be good, aside from otherwise noted external issues