reimplement 'f' move motion more efficiently, not leaving the LineGap.t data structure while iterating to next count

fcore/normal-mode/normal-mode.sml

@@ -571,9 +571,7 @@ struct
         parseMoveToChr (1, app, Cursor.tillPrevChr, chrCmd)
     | #"y" => ParseYank.parseYank (strPos, str, count, app, chrCmd, time)
     | #"d" => ParseDelete.parseDelete (strPos, str, count, app, chrCmd, time)
-    | #"f" =>
-        (* to chr, forward *)
-        parseMoveToChr (count, app, Cursor.toNextChr, chrCmd)
+    | #"f" => (* to chr, forward *) NormalMove.toNextChr (app, count, chrCmd)
     | #"F" =>
         (* to chr, backward *)
         parseMoveToChr (count, app, Cursor.toPrevChr, chrCmd)

fcore/normal-mode/normal-move.sml

@@ -516,4 +516,18 @@ struct
         NormalFinish.buildTextAndClear
           (app, buffer, newCursorIdx, searchList, [], bufferModifyTime)
     end
+
+  fun toNextChr (app: app_type, count, chr) =
+    let
+      val {cursorIdx, buffer, searchList, bufferModifyTime, ...} = app
+      val buffer = LineGap.goToIdx (cursorIdx, buffer)
+      val newCursorIdx =
+        Cursor.toNextChrNew (buffer, cursorIdx, {findChr = chr, count = count})
+    in
+      if newCursorIdx = ~1 then
+        NormalFinish.clearMode app
+      else
+        NormalFinish.buildTextAndClear
+          (app, buffer, newCursorIdx, searchList, [], bufferModifyTime)
+    end
 end