fix(stepper): content not being rendered out initially with ivy (#15486)

Fixes the stepper's content not being shown on the first render with Ivy, because we assume that the template with be present on init.

Author: crisbeto

src/cdk/stepper/stepper.ts

@@ -122,7 +122,7 @@ export class CdkStep implements OnChanges {
   @ContentChild(CdkStepLabel) stepLabel: CdkStepLabel;
 
   /** Template for step content. */
-  @ViewChild(TemplateRef) content: TemplateRef<any>;
+  @ViewChild(TemplateRef, {static: true}) content: TemplateRef<any>;
 
   /** The top level abstract control of the step. */
   @Input() stepControl: AbstractControl;