refactor(schematics): allow subscription sharing on isHandset$ (#16453)

Author: jerome-nelson

src/material/schematics/ng-generate/nav/files/__path__/__name@dasherize@if-flat__/__name@dasherize__.component.ts.template

@@ -1,7 +1,7 @@
 import { Component<% if(!!viewEncapsulation) { %>, ViewEncapsulation<% }%><% if(changeDetection !== 'Default') { %>, ChangeDetectionStrategy<% }%> } from '@angular/core';
 import { BreakpointObserver, Breakpoints } from '@angular/cdk/layout';
 import { Observable } from 'rxjs';
-import { map } from 'rxjs/operators';
+import { map, share } from 'rxjs/operators';
 
 @Component({
   selector: '<%= selector %>',<% if(inlineTemplate) { %>
@@ -20,7 +20,8 @@ export class <%= classify(name) %>Component {
 
   isHandset$: Observable<boolean> = this.breakpointObserver.observe(Breakpoints.Handset)
     .pipe(
-      map(result => result.matches)
+      map(result => result.matches),
+      share()
     );
 
   constructor(private breakpointObserver: BreakpointObserver) {}