The bug

Functions in data packs now load before entity tags. This causes errors when loading a data pack for the first time.

To reproduce:

1. Download the attached datapack Bug Datapack.zip and place in the world file.
2. /reload
   There is an error in the log stating there was an invalid entity.

   Failed to load function bug:error
   java.util.concurrent.CompletionException: java.lang.IllegalArgumentException: Whilst parsing command on line 1: Invalid or unknown entity type 'bug:cat' at position 12: ...y @e[type=<--[HERE]
   	...
   Caused by: java.lang.IllegalArgumentException: Whilst parsing command on line 1: Invalid or unknown entity type 'bug:cat' at position 12: ...y @e[type=<--[HERE]
   	...
   

3. /reload one more time, and see that the error doesn't appear.

From this, we can conclude that the function is loading before the tag, as if the tag was invalid, it would be invalid in the function the second time. However, the second time it is not invalid, so therefore it must have been loaded.