[video_player] Calls onDestroy instead of initialize in onDetachedFromEngine

[0xZOne]

In the onDetachedFromEngine function, the onDestroy method should be called instead of the initialize method, even though the implementation of the two functions is no different.

  private void onDestroy() {
    // The whole FlutterView is being destroyed. Here we release resources acquired for all
    // instances
    // of VideoPlayer. Once https://github.com/flutter/flutter/issues/19358 is resolved this may
    // be replaced with just asserting that videoPlayers.isEmpty().
    // https://github.com/flutter/flutter/issues/20989 tracks this.
    disposeAllPlayers();
  }

  public void initialize() {
    disposeAllPlayers();
  }

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[flutter-dashboard]

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[stuartmorgan-g]

test-exempt: code refactor with no semantic change

[stuartmorgan-g]

Calls

(Please see the style guide linked from the PR checklist.)

[0xZOne]

done.

[stuartmorgan-g]

Please see the docs linked from the checklist on how to update a changelog containing NEXT.

[0xZOne]

done.

[Hixie]

test-exempt: code refactor with no semantic change

[camsim99]

LGTM