[Display Layout] Add delete button (#2251)

* Add delete button in the toolbar for removing items

* Mutate composition if there are no telemetry objects. Select the parent layout after deleting an item.

* Saving work

* Watch for index in the components and update it in the context.

* Select the parent after a composition is removed.

* Address reviewer's feedback.
- Rename mutatComposition() to removeFromComposition().
- Inline logic for filtering composition
- Use separate branches for each item type in trackItem().

* Address reviewer's requested changes

src/plugins/displayLayout/components/TelemetryView.vue

@@ -160,6 +160,15 @@
                 domainObject: undefined
             }
         },
+        watch: {
+            index(newIndex) {
+                if (!this.context) {
+                    return;
+                }
+
+                this.context.index = newIndex;
+            }
+        },
         methods: {
             requestHistoricalData() {
                 let bounds = this.openmct.time.bounds();
@@ -205,13 +214,13 @@
                 this.requestHistoricalData();
                 this.subscribeToObject();
 
-                let context = {
+                this.context = {
                     item: domainObject,
                     layoutItem: this.item,
                     index: this.index
                 };
                 this.removeSelectable = this.openmct.selection.selectable(
-                    this.$el, context, this.initSelect);
+                    this.$el, this.context, this.initSelect);
             }
         },
         mounted() {