…e 'main' highlighter on a large file.

Before this patch:

num  calls                time                       self            name
-----------------------------------------------------------------------------------
 1)    3       33410.81 11136.94   98.51%  19277.07  6425.69   56.84%  _zsh_highlight_main_highlighter_highlight_list
19)    1       33916.21 33916.21  100.00%      5.27     5.27    0.02%  _zsh_highlight

With this patch:

num  calls                time                       self            name
-----------------------------------------------------------------------------------
 1)    3       27167.49  9055.83   98.17%  18754.77  6251.59   67.77%  _zsh_highlight_main_highlighter_highlight_list
19)    1       27674.40 27674.40  100.00%      5.39     5.39    0.02%  _zsh_highlight

----

And if test-zprof.zsh is changed to not set interactivecomments:

num  calls                time                       self            name
-----------------------------------------------------------------------------------
 1) 13360       36029.12     2.70   83.56%  30304.23     2.27   70.28%  _zsh_highlight_main_highlighter_highlight_argument
21)    1       43117.76 43117.76  100.00%      4.52     4.52    0.01%  _zsh_highlight

num  calls                time                       self            name
-----------------------------------------------------------------------------------
 1) 13360       14782.89     1.11   68.12%   9163.42     0.69   42.23%  _zsh_highlight_main_highlighter_highlight_argument
21)    1       21699.93 21699.93  100.00%      4.17     4.17    0.02%  _zsh_highlight

num  calls                time                       self            name
-----------------------------------------------------------------------------------
 1)    3       25689.17  8563.06   98.15%  18422.01  6140.67   70.38%  _zsh_highlight_main_highlighter_highlight_list
 2) 32390        5706.13     0.18   21.80%   2315.68     0.07    8.85%  _zsh_highlight_main_highlighter_highlight_argument
19)    1       26173.33 26173.33  100.00%      5.27     5.27    0.02%  _zsh_highlight

Interestingly, if I make the change in this diff to
_zsh_highlight_main_highlighter_highlight_double_quote —

>     diff --git a/highlighters/main/main-highlighter.zsh b/highlighters/main/main-highlighter.zsh
>     index da6ab2b..bb17618 100644
>     --- a/highlighters/main/main-highlighter.zsh
>     +++ b/highlighters/main/main-highlighter.zsh
>     @@ -1462,10 +1462,13 @@ _zsh_highlight_main_highlighter_highlight_double_quote()
>        local i j k ret style
>        reply=()
>
>     -  for (( i = $1 + 1 ; i <= $#arg ; i += 1 )) ; do
>     +  (( i = $1 ))
>     +  while (( ++i <= $#arg )); do
>     +    i=${arg[(ib.i.)[\"\`\$\\\\${histchars[1]}]]}
>          (( j = i + start_pos - 1 ))
>          (( k = j + 1 ))
>          case "$arg[$i]" in
>     +      ("")  break;;
>            ('"') break;;
>            ('`') saved_reply=($reply)
>                  _zsh_highlight_main_highlighter_highlight_backtick $i

— it actually makes things measurably slower (!), even on input that has
a large number of pasted double-quoted strings: on «BUFFER=": ${(r.8*1500..foo"bar".):-}"»
the slowdown is (1123.24ms / 1091.06ms = 1.0295).  Therefore, I won't be
committing that change.