Before, we were only completing columns in a JOIN in a "Binary Expression".
But for TreeSitter to recognize a Binary Expression, we need an= sign.

So this wouldn't complete, since there's no= sign:
select * from users u join posts p on u.{}

Now, we're checking for theON node, and completing columns if we're after it.

Note: Multiple joins are each individual join clauses with their own separate ON nodes, so there's no intereference:

select*from users ujoin posts ponu.id=post.user_id-- join clause 1join {}-- join clause 2

We won't autocompete a column, since there's no ON node in join cluase 2 🥳