Fixed #25893 -- Corrected custom lookups example.

There are a couple of notable things going on. First, ``AbsoluteValueLessThan``

isn't calling ``process_lhs()``. Instead it skips the transformation of the

``lhs`` done by ``AbsoluteValue`` and uses the original ``lhs``. That is, we

want to get ``27`` not ``ABS(27)``. Referring directly to ``self.lhs.lhs`` is

safe as ``AbsoluteValueLessThan`` can be accessed only from the

``AbsoluteValue`` lookup, that is the ``lhs`` is always an instance of

``AbsoluteValue``.

want to get ``"experiments"."change"`` not ``ABS("experiments"."change")``.

Referring directly to ``self.lhs.lhs`` is safe as ``AbsoluteValueLessThan``

can be accessed only from the ``AbsoluteValue`` lookup, that is the ``lhs``

is always an instance of ``AbsoluteValue``.

Notice also that  as both sides are used multiple times in the query the params

need to contain ``lhs_params`` and ``rhs_params`` multiple times.