fix(button): apply requested changes

projects/igniteui-angular/src/lib/directives/button/button-base.ts

@@ -1,7 +1,6 @@
-import { AfterViewInit, Directive, ElementRef, EventEmitter, HostBinding, HostListener, Inject, Input, Optional, Output, booleanAttribute } from '@angular/core';
+import { Directive, ElementRef, EventEmitter, HostBinding, HostListener, Inject, Input, Optional, Output, booleanAttribute } from '@angular/core';
 import { DisplayDensityBase, DisplayDensityToken, IDisplayDensityOptions } from '../../core/density';
 import { mkenum } from '../../core/utils';
-import { fromEvent } from 'rxjs';
 
 export const IgxBaseButtonType = /*@__PURE__*/mkenum({
     Flat: 'flat',
@@ -10,7 +9,7 @@ export const IgxBaseButtonType = /*@__PURE__*/mkenum({
 });
 
 @Directive()
-export abstract class IgxButtonBaseDirective extends DisplayDensityBase implements AfterViewInit {
+export abstract class IgxButtonBaseDirective extends DisplayDensityBase {
     /**
      * Emitted when the button is clicked.
      */
@@ -59,7 +58,7 @@ export abstract class IgxButtonBaseDirective extends DisplayDensityBase implemen
      * ```
      */
     @HostBinding('class.igx-button--focused')
-    public focused = false;
+    protected focused = false;
 
     /**
       * Enables/disables the button.
@@ -90,16 +89,11 @@ export abstract class IgxButtonBaseDirective extends DisplayDensityBase implemen
         super(_displayDensityOptions, element);
     }
 
-    public ngAfterViewInit() {
-        fromEvent(this.nativeElement, 'keyup').subscribe((event: KeyboardEvent) => {
-            this.updateOnKeyUp(event)
-        });
-    }
-
     /**
      * @hidden
      * @internal
      */
+    @HostListener('keyup', ['$event'])
     protected updateOnKeyUp(event: KeyboardEvent) {
         if (event.key === "Tab") {
             this.focused = true;