AppliedUndef.is_number = False

[smichr]

This PR changes is_number behavior and AccumBound.contains error handling

b: f(1).is_number is now False when f is an AppliedUndef; the former foo.is_number is now equivalent to not foo.free_symbols. is_number is generally used to detect expressions that might be evaluated.
m: AccumBounds.contains only raises an error if the condition is unevaluated

• is_number now is only True for something that will evaluate to a number (though it may not do so with precision).
• is_comparable (for reference) is only True if something is a number and evaluates with precision
• The contains method of AccumBounds was overly optimistic since something being a number does not guarantee that the condition tested will be evaluated. An error is now raised if the condition is not evaluated and the and separating args in the And was changed to a comma: And(c1, c2) not And(c1 and c2).

fixes #5033
fixes #6646