classes.dispatch: Add word for checking class participation

Used to determine whether a dispatch specifier depends on a specific class.
Used for dependency checking.

core/classes/dispatch/class/class.factor

@@ -51,3 +51,6 @@ M: class-specializer (classes-intersect?)
 
 M: class-specializer add-depends-on-class
     class>> add-depends-on-class ;
+
+M: class-specializer dispatch-depends-on?
+    class>> class= ;

core/classes/dispatch/covariant-tuples/covariant-tuples.factor

@@ -78,3 +78,6 @@ M: covariant-tuple dispatch-predicate-def
     [ 1 + swap '{ [ _ npick _ instance? not ] [ f ] } ] map-index
     [ t ] suffix
     '[ _ cond ] ;
+
+M: covariant-tuple dispatch-depends-on?
+    classes>> member? ;

core/classes/dispatch/dispatch.factor

@@ -31,3 +31,6 @@ GENERIC: dispatch-arity ( dispatch-type -- n )
 ! type at index.
 GENERIC: nth-dispatch-applicable? ( class index dispatch-type -- ? )
 GENERIC: dispatch-predicate-def ( dispatch-type -- quot )
+
+! Return whether the dispatch specifier depends on the given class
+GENERIC: dispatch-depends-on? ( class dispatch-type -- ? )

core/classes/dispatch/eql/eql.factor

@@ -37,3 +37,6 @@ M: eql-specializer left-dispatch<=
 M: eql-specializer (classes-intersect?)
     { { [ over eql-specializer? ] [ [ obj>> ] same? ] }
       [ obj>> class-of classes-intersect? ] } cond ;
+
+M: eql-specializer dispatch-depends-on?
+    obj>> class-of class= ;