Improve how intersections are classified as weak types

[Andarist]

fixes #56995

[Andarist]

The idea behind the fix is that an empty object type should not be considered to be weak on its own. That's comes from the pre-existing requirement for weak types:

resolved.properties.length > 0 && every(resolved.properties, p => !!(p.flags & SymbolFlags.Optional))

However, when it's intersected with a weak type that should not make it, out of a sudden, non-weak. The new logic still maintains the invariant that an intersection of many empty interfaces is not considered to be weak (it should obey the same rules as a single empty interface).

All of that doesn't change the definition put in the existing code comment:

    /**
     * A type is 'weak' if it is an object type with at least one optional property
     * and no required properties, call/construct signatures or index signatures
     */

Actually, the old behavior wasn't enforcing those rules for intersections precisely enough. The proposed adjustment is closer to checking the intersection as a single type with a flat list of properties instead of checking separate types and combining those results "blindly". I think it's more accurate to do it this way because for most purposes an intersection shouldn't be distinguishable from the same type with a "flattened" list of properties.