Remove redundant Func.resolve_expression and adjust CombinedExpression to
delegate source expression resolving to super() to perform checks against
allows_composite_expressions in a single location.
Thanks Lily Foote and Simon Charette for reviews and mentoring
this Google Summer of Code 2024 project.
Co-authored-by: Simon Charette <charette.s@gmail.com>
Co-authored-by: Lily Foote <code@lilyf.org>