delete 'nextMatch' function in search-list.sml, and refactor other code to use alternative function

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

@@ -766,7 +766,8 @@ struct
   fun deleteToNextMatch (app: app_type, count, time) =
     let
       val {cursorIdx, searchList, ...} = app
-      val newCursorIdx = SearchList.nextMatch (cursorIdx, searchList, count)
+      val newCursorIdx =
+        PersistentVector.nextMatch (cursorIdx, searchList, count)
     in
       if newCursorIdx = ~1 orelse newCursorIdx <= cursorIdx then
         NormalFinish.clearMode app

fcore/normal-mode/normal-yank.sml

@@ -168,7 +168,7 @@ struct
   fun yankToNextMatch (app: app_type, count) =
     let
       val {cursorIdx, searchList, buffer, ...} = app
-      val high = SearchList.nextMatch (cursorIdx, searchList, count)
+      val high = PersistentVector.nextMatch (cursorIdx, searchList, count)
     in
       if high = ~1 orelse high <= cursorIdx then
         NormalFinish.clearMode app

fcore/persistent-vector.sml

@@ -178,4 +178,11 @@ struct
         else
           loopNextMatch (start, finish, tree, count - 1)
       end
+
+  fun getLast tree =
+    case tree of
+      LEAF (values, _) => 
+        Vector.sub (values, Vector.length values - 1)
+    | BRANCH (nodes, _) =>
+        getLast (Vector.sub (nodes, Vector.length nodes - 1))
 end

fcore/search-list/search-list.sml

@@ -122,7 +122,5 @@ struct
     else
       (buffer, PersistentVector.empty)
 
-  fun nextMatch (cursorIdx, searchList, count) = raise Fail "todo: reimplement"
-
   fun prevMatch (cursorIdx, searchList, count) = raise Fail "todo: reimplement"
 end