style: consistent figure style (#3060)

Use a consistent style for the "good / bad" examples:

- start the code at the far left of each box
- keep a little space between the top of the box & the label

pkgs/racket-doc/scribblings/style/textual.scrbl

@@ -30,21 +30,24 @@ your code.
  (define (conversion f)
    (* 5/9 (- f 32)))
 ]
- @filebox[@tt{really bad}
+ @racketmod[#:file
- @codeblock{#lang racket
+ @tt{really bad}
+ racket
+
  (define (conversion f)
    (* 5/9 (- f 32)
      )
    )
- }]
+ ]
 ]
 
 You are allowed to place all closing parenthesis on a line by itself at the
 end of long sequences, be those definitions or pieces of data.
 
 @compare[
- @filebox[@tt{acceptable}
+ @racketmod[#:file
- @codeblock{#lang racket
+ @tt{acceptable}
+ racket
  (define modes
    '(edit
      help
@@ -53,9 +56,10 @@ end of long sequences, be those definitions or pieces of data.
      trace
      step
      ))
- }]
+ ]
- @filebox[@tt{also acceptable}
+ @racketmod[#:file
- @codeblock{#lang racket
+ @tt{also acceptable}
+ racket
  (define turn%
    (class object%
      (init-field state)
@@ -68,7 +72,7 @@ end of long sequences, be those definitions or pieces of data.
      (define/public (is-placable? place)
        (send state legal? place))
      ))
- }]
+ ]
 ]
  Doing so is most useful when you expect to add, delete, or swap items in
  such sequences.
@@ -383,12 +387,13 @@ space between the two, even if they’re separated by parentheses.
  (define (f x g)
    [(< x 3) (g (g 3))])
 ]
- @filebox[@tt{bad}
+ @racketmod[#:file
- @codeblock{#lang racket
+ @tt{bad}
+ racket
 
  (define(f x g)
    [(< x 3)(g(g 3))])
- }]
+ ]
 ]