docs: update Angular integration examples for modern APIs

[ArturQuirino]

Summary

Updates the Angular integration docs so examples follow current Angular patterns: signal-based viewChild / input() and teardown with inject(DestroyRef) instead of @ViewChild, @Input(), and ngOnDestroy.

What changed

• Basic setup — viewChild.required, AfterViewInit, and inject(DestroyRef).onDestroy() for superdoc.destroy(); SuperDoc is created in ngAfterViewInit so the template ref exists.
• Full component — input.required() / input() for inputs; same viewChild + DestroyRef pattern; document and user read via this.document() / this.user().
• Handle file uploads — Restores full imports at the top of the snippet; same viewChild + DestroyRef cleanup; selector uses this.editorRef().nativeElement.

Why

Keeps the Getting Started Angular page aligned with modern Angular and copy-pasteable for recent projects.

Test plan

• pnpm run check:imports
• pnpm run dev:docs — verify Angular Integration page renders and snippets look correct

[caio-pizzol]

@ArturQuirino nice cleanup — the code is correct and consistent across all three snippets, and snippet 3 quietly fixes a missing-imports bug from the old version.

one ask: these examples need Angular 17.1+ (signal-based viewChild() and input() shipped in 17.1). the old examples worked on much older versions. anyone on older Angular who copy-pastes will get errors they won't understand. worth adding a one-liner under the intro on line 7? something like:

Examples use signal-based APIs (viewChild(), input()) introduced in Angular 17.1. For older Angular versions, swap to the decorator-based equivalents (@ViewChild, @Input).

also left a small nit inline on typing the element ref.

[caio-pizzol]

small nit (applies to all three snippets): typing ElementRef<HTMLDivElement> gives nativeElement a real type instead of any. since the template is a <div>, it's a free win.

Suggested change

	private readonly editorRef = viewChild.required<ElementRef>('editor');
	private readonly editorRef = viewChild.required<ElementRef<HTMLDivElement>>('editor');