Ensure ClauseAdapter treats FunctionElement as a ColumnElement

Ensure ClauseAdapter treats FunctionElement as a ColumnElement

Fixed regression where use of an unnamed SQL expression such as a SQL
function would raise a column targeting error if the query itself were
using joinedload for an entity and was also being wrapped in a subquery by
the joinedload eager loading process.

Fixes: #6086
Change-Id: I22cf4d6974685267c4f903bd7639be8271c6c1ef