Make tree items more actionable and add AppAction for expanding the object tree (#5997)

* style: add `visibility` to tree expand triangles

- The purpose of this is so that Playwright can perform actionability checks on the tree items. This will make operations involving expanding tree items much easier to perform in e2e.

* feat(e2e): Add AppAction to expand the entire tree

* fix: wait for loading indicator

* test: add test for `expandEntireTree`

* test: update `expandEntireTree` and tree selectors

- Use dynamic aria-label for different tree implementations

- Get rid of CSS ids which are only for testing

- Update percy tree scope selector

* chore(lint): remove unused variable

* refactor(e2e): update tree locators

Co-authored-by: John Hill <john.c.hill@nasa.gov>

src/api/forms/components/controls/Locator.vue

@@ -22,7 +22,6 @@
 
 <template>
 <mct-tree
-    id="locator-tree"
     :is-selector-tree="true"
     :initial-selection="model.parent"
     @tree-item-selection="handleItemSelection"

src/styles/_controls.scss

@@ -270,9 +270,11 @@ button {
     flex: 0 0 auto;
     width: $d;
     position: relative;
+    visibility: hidden;
 
     &.is-enabled {
         cursor: pointer;
+        visibility: visible;
 
         &:hover {
             color: $colorDisclosureCtrlHov;

src/ui/layout/Layout.vue

@@ -79,9 +79,7 @@
             <multipane
                 type="vertical"
             >
-                <pane
-                    id="tree-pane"
-                >
+                <pane>
                     <mct-tree
                         ref="mctTree"
                         :sync-tree-navigation="triggerSync"

src/ui/layout/mct-tree.vue

@@ -41,6 +41,7 @@
         ref="mainTree"
         class="c-tree-and-search__tree c-tree"
         role="tree"
+        :aria-label="getAriaLabel"
         aria-expanded="true"
     >
 
@@ -192,6 +193,9 @@ export default {
         focusedItems() {
             return this.activeSearch ? this.searchResultItems : this.treeItems;
         },
+        getAriaLabel() {
+            return this.isSelectorTree ? "Create Modal Tree" : "Main Tree";
+        },
         pageThreshold() {
             return Math.ceil(this.mainTreeHeight / this.itemHeight) + ITEM_BUFFER;
         },