fix: mark virtual scroll viewport queries as static

Author: kara

src/cdk/scrolling/virtual-scroll-viewport.spec.ts

@@ -834,8 +834,8 @@ function triggerScroll(viewport: CdkVirtualScrollViewport, offset?: number) {
   encapsulation: ViewEncapsulation.None,
 })
 class FixedSizeVirtualScroll {
-  @ViewChild(CdkVirtualScrollViewport) viewport: CdkVirtualScrollViewport;
-  @ViewChild(CdkVirtualForOf) virtualForOf: CdkVirtualForOf<any>;
+  @ViewChild(CdkVirtualScrollViewport, {static: true}) viewport: CdkVirtualScrollViewport;
+  @ViewChild(CdkVirtualForOf, {static: true}) virtualForOf: CdkVirtualForOf<any>;
 
   @Input() orientation = 'vertical';
   @Input() viewportSize = 200;
@@ -885,7 +885,7 @@ class FixedSizeVirtualScroll {
   encapsulation: ViewEncapsulation.None,
 })
 class FixedSizeVirtualScrollWithRtlDirection {
-  @ViewChild(CdkVirtualScrollViewport) viewport: CdkVirtualScrollViewport;
+  @ViewChild(CdkVirtualScrollViewport, {static: true}) viewport: CdkVirtualScrollViewport;
 
   @Input() orientation = 'vertical';
   @Input() viewportSize = 200;

src/cdk/scrolling/virtual-scroll-viewport.ts

@@ -76,7 +76,7 @@ export class CdkVirtualScrollViewport extends CdkScrollable implements OnInit, O
             Promise.resolve().then(() => this.ngZone.run(() => observer.next(index)))));
 
   /** The element that wraps the rendered content. */
-  @ViewChild('contentWrapper') _contentWrapper: ElementRef<HTMLElement>;
+  @ViewChild('contentWrapper', {static: true}) _contentWrapper: ElementRef<HTMLElement>;
 
   /** A stream that emits whenever the rendered range changes. */
   renderedRangeStream: Observable<ListRange> = this._renderedRangeSubject.asObservable();