refactor(docs-infra): get rid of `on` component input (#26947)

Compiling with Ivy doesn't seem to allow input names starting with `on`.

PR Close #26947

aio/src/app/app.component.html

@@ -61,7 +61,7 @@
         (docInserted)="onDocInserted()"
         (docRendered)="onDocRendered()">
     </aio-doc-viewer>
-    <aio-dt [on]="dtOn" [(doc)]="currentDocument"></aio-dt>
+    <aio-dt *ngIf="dtOn" [(doc)]="currentDocument"></aio-dt>
   </main>
 
 </mat-sidenav-container>

aio/src/app/layout/doc-viewer/dt.component.ts

@@ -4,17 +4,16 @@ import { DocumentContents } from 'app/documents/document.service';
 @Component({
   selector: 'aio-dt',
   template: `
-  <div *ngIf="on">
-    <hr>
-    <textarea #dt [value]="text" rows="10" cols="80"></textarea>
-    <br/>
-    <button (click)="dtextSet()">Show change</button>
-  </div>
+    <div>
+      <hr>
+      <textarea #dt [value]="text" rows="10" cols="80"></textarea>
+      <br/>
+      <button (click)="dtextSet()">Show change</button>
+    </div>
   `
 })
 export class DtComponent {
 
-  @Input() on = false;
   @Input() doc: DocumentContents;
   @Output() docChange = new EventEmitter<DocumentContents>();