rerender through callback instead of after modifying model

this way rendering is centralized and we can better rerender
from interaction in the autocompleter
(we didn't have access to caret before)

src/editor/model.js

@@ -17,12 +17,13 @@ limitations under the License.
 import {diffAtCaret, diffDeletion} from "./diff";
 
 export default class EditorModel {
-    constructor(parts, partCreator) {
+    constructor(parts, partCreator, updateCallback) {
         this._parts = parts;
         this._partCreator = partCreator;
         this._activePartIdx = null;
         this._autoComplete = null;
         this._autoCompletePartIdx = null;
+        this._updateCallback = updateCallback;
     }
 
     _insertPart(index, part) {
@@ -90,7 +91,7 @@ export default class EditorModel {
         const caretOffset = diff.at + (diff.added ? diff.added.length : 0);
         const newPosition = this._positionForOffset(caretOffset, true);
         this._setActivePart(newPosition);
-        return newPosition;
+        this._updateCallback(newPosition);
     }
 
     _setActivePart(pos) {
@@ -116,10 +117,12 @@ export default class EditorModel {
 
     _onAutoComplete = ({replacePart, replaceCaret, close}) => {
         this._replacePart(this._autoCompletePartIdx, replacePart);
+        const index = this._autoCompletePartIdx;
         if (close) {
             this._autoComplete = null;
             this._autoCompletePartIdx = null;
         }
+        this._updateCallback(new DocumentPosition(index, replaceCaret));
     }
 
     /*