Joining table function against itself

[max-hoffman]

I am not sure this DiffTableFunctionScriptTest should succeed. The table/column resolving should be ambiguous.

SELECT to_pk, to_c1, to_c2, from_pk, from_c1, from_c2, diff_type
from dolt_diff(@Commit1, @Commit2, 't')
join dolt_diff(@Commit1, @Commit3, 't') on to_pk = to_pk