'main': Highlight lone '!' correctly: it's not a history expansion.

While here, also add a test for the '!' reserved word (which is highlighted
since c216242b).

highlighters/main/main-highlighter.zsh

@@ -342,7 +342,9 @@ _zsh_highlight_main_highlighter()
                             # (For array assignments, the command doesn't start until the ")" token.)
                             next_word+=':start:'
                           fi
-                        elif [[ $arg[0,1] == $histchars[0,1] || $arg[0,1] == $histchars[2,2] ]]; then
+                        elif [[ $arg[0,1] = $histchars[0,1] ]] && (( $#arg[0,2] == 2 )); then
+                          style=$ZSH_HIGHLIGHT_STYLES[history-expansion]
+                        elif [[ $arg[0,1] == $histchars[2,2] ]]; then
                           style=$ZSH_HIGHLIGHT_STYLES[history-expansion]
                         elif [[ -n ${(M)ZSH_HIGHLIGHT_TOKENS_COMMANDSEPARATOR:#"$arg"} ]]; then
                           if [[ $this_word == *':regular:'* ]]; then
@@ -414,7 +416,7 @@ _zsh_highlight_main_highlighter()
         [*?]*|*[^\\][*?]*)
                  $highlight_glob && style=$ZSH_HIGHLIGHT_STYLES[globbing] || style=$ZSH_HIGHLIGHT_STYLES[default];;
         *)       if false; then
-                 elif [[ $arg[0,1] = $histchars[0,1] ]]; then
+                 elif [[ $arg[0,1] = $histchars[0,1] ]] && (( $#arg[0,2] == 2 )); then
                    style=$ZSH_HIGHLIGHT_STYLES[history-expansion]
                  elif [[ -n ${(M)ZSH_HIGHLIGHT_TOKENS_COMMANDSEPARATOR:#"$arg"} ]]; then
                    if [[ $this_word == *':regular:'* ]]; then

highlighters/main/test-data/history-expansion.zsh

@@ -28,10 +28,12 @@
 # -------------------------------------------------------------------------------------------------
 
 ZSH_HIGHLIGHT_STYLES[default]=$unused_highlight
-BUFFER='!foo bar !baz'
+BUFFER='!foo bar !baz ! ; !'
 
 expected_region_highlight=(
   "1 4 $ZSH_HIGHLIGHT_STYLES[history-expansion]" # !foo
   "6 8 $ZSH_HIGHLIGHT_STYLES[default]" # bar
   "10 13 $ZSH_HIGHLIGHT_STYLES[history-expansion]" # !baz
+  "15 15 $ZSH_HIGHLIGHT_STYLES[default]" # ! (before the semicolon)
+  "19 19 $ZSH_HIGHLIGHT_STYLES[reserved-word]" # ! (after the semicolon)
 )