reimplement 'df' motion as per previous commits, and add a new test for 'df' motion to check that cursor does not land on a 'newline following a non-newline' position, after deleting using 'df<char>'

fcore/normal-mode/make-normal-delete.sml

@@ -648,7 +648,7 @@ struct
 
   fun deleteToFirstNonSpaceChr (app: app_type, time) =
     let
-      val {buffer, cursorIdx, windowWidth, windowHeight, startLine, ...} = app
+      val {buffer, cursorIdx, ...} = app
 
       (* move LineGap and buffer to start of line *)
       val buffer = LineGap.goToIdx (cursorIdx, buffer)
@@ -712,6 +712,31 @@ struct
       , time
       )
 
+  fun deleteToNextChr (app: app_type, count, chr, time) =
+    let
+      val {buffer, cursorIdx, ...} = 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
+        let
+          val length = newCursorIdx - cursorIdx + 1
+          val buffer = LineGap.goToIdx (newCursorIdx, buffer)
+          val initialMsg = Fn.initMsgs (cursorIdx, length, buffer)
+          val buffer = LineGap.delete (cursorIdx, length, buffer)
+
+          val buffer = LineGap.goToIdx (cursorIdx, buffer)
+          val cursorIdx =
+            if Cursor.isOnNewlineAfterChr (buffer, cursorIdx) then cursorIdx - 1
+            else cursorIdx
+        in
+          finishAfterDeletingBuffer (app, cursorIdx, buffer, time, initialMsg)
+        end
+    end
+
   fun deleteToStart (app: app_type, time) : AppType.app_type =
     let
       val {cursorIdx, buffer, windowWidth, windowHeight, dfa, ...} = app