Add comprehensive suggestions to many commands.

All patterns now have suggestions, including recursive patterns.
Suggestions will suggest blocks and block states.
All masks now have suggestions, though mask intersections are not
yet supported due to issues with quotes strings.
EntityRemover and ItemFactory now also have completions, as well
as all RegistryConverters (though I am unsure how many are actually
used).

Also use paper's AsyncTabComplete event, if available.

worldedit-core/src/main/java/com/sk89q/worldedit/command/RegionCommands.java

@@ -89,7 +89,7 @@ public class RegionCommands {
     @Logging(REGION)
     public int set(Player player, EditSession editSession,
                    @Selection Region region,
-                   @Arg(desc = "The patter of blocks to set")
+                   @Arg(desc = "The pattern of blocks to set")
                        Pattern pattern) {
         RegionFunction set = new BlockReplace(editSession, pattern);
         RegionVisitor visitor = new RegionVisitor(region, set);