[player] Rename event method to `onMouseDown`

projects/player/src/app/components/key/key.component.html

-<button (mousedown)="onClick($event)" mat-stroked-button>{{character}}</button>
+<button (mousedown)="onMouseDown($event)" mat-stroked-button>{{character}}</button>

projects/player/src/app/components/key/key.component.ts

@@ -11,7 +11,7 @@ export class KeyComponent {
 
   constructor(private specialCharacterService: SpecialCharacterService) { }
 
-  onClick(event: MouseEvent): void {
+  onMouseDown(event: MouseEvent): void {
     this.specialCharacterService.inputCharacter(this.character);
     event.preventDefault();
   }