Return self when Variant.coerce_compared_value would return impl

Return self when Variant.coerce_compared_value would return impl

Fixed regression released in 1.1.5 due to :ticket:`3859` where
adjustments to the "right-hand-side" evaluation of an expression
based on :class:`.Variant` to honor the underlying type's
"right-hand-side" rules caused the :class:`.Variant` type
to be inappropriately lost, in those cases when we *do* want the
left-hand side type to be transferred directly to the right hand side
so that bind-level rules can be applied to the expression's argument.

Change-Id: Ia54dbbb19398549d654b74668753c4152599d900
Fixes: #3952