Provide a submodule for begin-encourage-inline.

As suggested in a comment in the file.

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

@@ -2957,7 +2957,11 @@ syntactic forms or languages that supply a more limited kind of
 
 Attaches a @racket['compiler-hint:cross-module-inline]
 @tech{syntax property} to each @racket[form], which is useful when a
-@racket[form] is a function definition. See @racket[define-values].}
+@racket[form] is a function definition. See @racket[define-values].
+
+The @racket[begin-encourage-inline] form is also provided by the
+@racketmodname[(submod racket/performance-hint begin-encourage-inline)] module,
+which has fewer dependencies than @racketmodname[racket/performance-hint].}
 
 @defform*/subs[[(define-inline id expr)
                 (define-inline (head args) body ...+)]

racket/collects/racket/performance-hint.rkt

@@ -2,14 +2,13 @@
 
 (require "private/performance-hint.rkt")
 
-;; Note: because of `define-inline''s dependencies, this module is pretty
-;;  heavyweight. If this becomes a problem, we can export a
-;;  `begin-encourage-inline' submodule (that only re-exports
-;;  `begin-encourage-inline'), to make it available without the overhead.
-
 (provide begin-encourage-inline
          define-inline)
 
+(module begin-encourage-inline '#%kernel
+  (#%require "private/performance-hint.rkt")
+  (#%provide begin-encourage-inline))
+
 (require (for-syntax syntax/parse syntax/define
                      racket/syntax racket/base)
          racket/stxparam)