This diagnostic group includes errors and warnings pertaining to the any type
syntax proposed in SE-0335.
any syntax draws a line between constraint types and existential or boxed
types.
For example, any Collection is a boxed type abstracting over a value of a
dynamic type that conforms to the protocol Collection, whereas the
Collection part is the conformance constraint imposed on the type of the
underlying value as well as a constraint type.
The distinction between a conformance constraint and a constraint type can be
clearly seen in classic generic syntax: <T: Collection>.
Constraint types exist to express conformances and have no meaning in relation to values.
func sillyFunction(collection: Collection) { // error
// ...
}