Add lint rule to ensure on prefix is only for event emitters

Fixes #4183

src/browser/selection/SelectionModel.test.ts

@@ -50,17 +50,17 @@ describe('SelectionModel', () => {
     it('should trim a portion of the selection when a part of it is trimmed', () => {
       model.selectionStart = [0, 0];
       model.selectionEnd = [10, 2];
-      model.onTrim(1);
+      model.handleTrim(1);
       assert.deepEqual(model.finalSelectionStart, [0, 0]);
       assert.deepEqual(model.finalSelectionEnd, [10, 1]);
-      model.onTrim(1);
+      model.handleTrim(1);
       assert.deepEqual(model.finalSelectionStart, [0, 0]);
       assert.deepEqual(model.finalSelectionEnd, [10, 0]);
     });
     it('should clear selection when it is trimmed in its entirety', () => {
       model.selectionStart = [0, 0];
       model.selectionEnd = [10, 0];
-      model.onTrim(1);
+      model.handleTrim(1);
       assert.deepEqual(model.finalSelectionStart, undefined);
       assert.deepEqual(model.finalSelectionEnd, undefined);
     });