Optional refs return input error when the input is not binding in composition or ref has no implicit binding

[snguyen64]

This error happens when:

• Don't provide a binding for that ref in the composition, OR
• The ref has no "implicit binding"

The optional ref should not error. If the binding doesn't exist, then we should not block synthesis since it is an optional ref.

[snguyen64]

Can assign to me and I can work on this