fix(animations): retain styling when transition destinations are changed (#12208)

Closes #9661
Closes #12208

modules/@angular/core/src/animation/animation_group_player.ts

@@ -88,7 +88,7 @@ export class AnimationGroupPlayer implements AnimationPlayer {
     this._started = false;
   }
 
-  setPosition(p: any /** TODO #9100 */): void {
+  setPosition(p: number): void {
     this._players.forEach(player => { player.setPosition(p); });
   }
 
@@ -100,4 +100,6 @@ export class AnimationGroupPlayer implements AnimationPlayer {
     });
     return min;
   }
+
+  get players(): AnimationPlayer[] { return this._players; }
 }

modules/@angular/core/src/animation/animation_player.ts

@@ -56,6 +56,6 @@ export class NoOpAnimationPlayer implements AnimationPlayer {
   finish(): void { this._onFinish(); }
   destroy(): void {}
   reset(): void {}
-  setPosition(p: any /** TODO #9100 */): void {}
+  setPosition(p: number): void {}
   getPosition(): number { return 0; }
 }

modules/@angular/core/src/animation/animation_sequence_player.ts

@@ -104,7 +104,9 @@ export class AnimationSequencePlayer implements AnimationPlayer {
     }
   }
 
-  setPosition(p: any /** TODO #9100 */): void { this._players[0].setPosition(p); }
+  setPosition(p: number): void { this._players[0].setPosition(p); }
 
   getPosition(): number { return this._players[0].getPosition(); }
+
+  get players(): AnimationPlayer[] { return this._players; }
 }

modules/@angular/core/src/animation/animation_style_util.ts

@@ -84,6 +84,8 @@ export function balanceAnimationKeyframes(
     firstKeyframe.styles.styles.push(extraFirstKeyframeStyles);
   }
 
+  collectAndResolveStyles(collectedStyles, [finalStateStyles]);
+
   return keyframes;
 }