Provide and document match-expander? and legacy-match-expander?.

pkgs/racket-pkgs/racket-doc/scribblings/reference/match.scrbl

@@ -630,6 +630,13 @@ Like @racket[prop:match-expander], but for the legacy match syntax.
 This binding is provided @racket[for-syntax].
 }
 
+@deftogether[[
+@defproc[(match-expander? [v any/c]) boolean?]
+@defproc[(legacy-match-expander? [v any/c]) boolean?]]]{
+Predicates for values which implement the appropriate match expander
+properties.
+}
+
 
 @defparam[match-equality-test comp-proc (any/c any/c . -> . any)]{
 

racket/collects/racket/match/match.rkt

@@ -10,13 +10,15 @@
          (for-syntax racket/lazy-require
                      (only-in "stxtime.rkt"
                               match-...-nesting
+                              match-expander?
+                              legacy-match-expander?
                               prop:match-expander
                               prop:legacy-match-expander)))
 
 (begin-for-syntax
   (lazy-require [racket/match/parse (parse)]))
 
-(provide (for-syntax match-...-nesting
+(provide (for-syntax match-...-nesting match-expander? legacy-match-expander?
                      prop:match-expander prop:legacy-match-expander)
          match-equality-test
          define-match-expander