fix(cdk-experimental/accordion): fix disabled trigger button can't be focused when skipDisabled=false (#31379)

Author: ok7sai

src/cdk-experimental/accordion/accordion.ts

@@ -93,6 +93,8 @@ export class CdkAccordionPanel {
     '[attr.aria-expanded]': 'pattern.expanded()',
     '[attr.aria-controls]': 'pattern.controls()',
     '[attr.aria-disabled]': 'pattern.disabled()',
+    '[attr.inert]': 'hardDisabled() ? true : null',
+    '[attr.disabled]': 'hardDisabled() ? true : null',
     '[attr.tabindex]': 'pattern.tabindex()',
     '(keydown)': 'pattern.onKeydown($event)',
     '(pointerdown)': 'pattern.onPointerdown($event)',
@@ -115,6 +117,13 @@ export class CdkAccordionTrigger {
   /** Whether the trigger is disabled. */
   disabled = input(false, {transform: booleanAttribute});
 
+  /**
+   * Whether this trigger is completely inaccessible.
+   *
+   * TODO(ok7sai): Consider move this to UI patterns.
+   */
+  readonly hardDisabled = computed(() => this.pattern.disabled() && this.pattern.tabindex() < 0);
+
   /** The accordion panel pattern controlled by this trigger. This is set by CdkAccordionGroup. */
   readonly accordionPanel: WritableSignal<AccordionPanelPattern | undefined> = signal(undefined);