chore(api): internal updates required for stencil 2 upgrade (#21889)

Stencil 2 is removing deprecated APIs, and these are the remaining ones Ionic has been using.

core/src/components/header/header.tsx

@@ -49,7 +49,7 @@ export class Header implements ComponentInterface {
     await this.checkCollapsibleHeader();
   }
 
-  componentDidUnload() {
+  disconnectedCallback() {
     this.destroyCollapsibleHeader();
   }