PR16263: Implement current direction of core issue 1376. Binding a reference to
the result of a cast-to-reference-type lifetime-extends the object to which the
reference inside the cast binds.

This requires us to look for subobject adjustments on both the inside and the
outside of the MaterializeTemporaryExpr when looking for a temporary to
lifetime-extend (which we also need for core issue 616, and possibly 1213).