fix(menu): properly implement selected state

Before, I set the focused, actively-keyboard-interacted, or pressed element as visual selected state. That doesn't seem to be how GMDC handles it and created problems down the line with md-select where we could not show the currently-selected item + keyboard navigation at the same time.

This CL brings the behavior in line with GMDC and fixes this problem down the line for select.

Also in this CL I add the selected state to sub-menu-item when it's open

PiperOrigin-RevId: 519166067

list/lib/listitem/list-item.ts

@@ -82,9 +82,9 @@ export class ListItemEl extends LitElement implements ListItem {
   @property({type: Number}) itemTabIndex = -1;
 
   /**
-   * Whether or not the element is in the selected visual state. When active,
-   * tabindex is set to 0, and in some list item variants (like md-list-item),
-   * focuses the underlying item.
+   * Whether or not the element is actively being interacted with by md-list.
+   * When active, tabindex is set to 0, and in some list item variants (like
+   * md-list-item), focuses the underlying item.
    */
   @property({type: Boolean, reflect: true}) active = false;
 

menu/lib/menuitem/_menu-item.scss

@@ -36,9 +36,7 @@ $_custom-property-prefix: 'menu';
   }
 
   .list-item {
-    :host([active]) &,
-    :host(:active) &,
-    &:focus {
+    :host([selected]) & {
       background-color: var(--_list-item-selected-container-color);
     }
   }

menu/lib/submenuitem/sub-menu-item.ts

@@ -44,6 +44,10 @@ export class SubMenuItem extends MenuItemEl {
    */
   @property({type: Number, attribute: 'hover-close-delay'})
   hoverCloseDelay = 400;
+  /**
+   * Sets the item in the selected visual state when a submenu is opened.
+   */
+  @property({type: Boolean, reflect: true}) selected = false;
 
   @queryAssignedElements({slot: 'submenu', flatten: true})
   protected menus!: Menu[];
@@ -157,12 +161,14 @@ export class SubMenuItem extends MenuItemEl {
         e.reason.key === KEYDOWN_CLOSE_KEYS.ESCAPE) {
       e.stopPropagation();
       this.active = true;
+      this.selected = false;
       // It might already be active so manually focus
       this.listItemRoot.focus();
       return;
     }
 
     this.active = false;
+    this.selected = false;
   }
 
   protected async onSubMenuKeydown(e: KeyboardEvent) {
@@ -212,6 +218,7 @@ export class SubMenuItem extends MenuItemEl {
     this.dispatchEvent(new DeactivateItemsEvent());
     this.dispatchEvent(new DeactivateTypeaheadEvent());
     this.active = true;
+    this.selected = true;
 
     // This is the case of mouse hovering when already opened via keyboard or
     // vice versa
@@ -235,6 +242,7 @@ export class SubMenuItem extends MenuItemEl {
     menu.quick = true;
     menu.close();
     this.active = false;
+    this.selected = false;
     menu.addEventListener('closed', onClosed, {once: true});
   }