Mouse and Pointer Events are called incorrectly in ScrollView with XRUIInputModule

When using UI Toolkit, typically it will install an event listener in the form of the `PanelEventHandler` component which intercepts events from the `XRUIInputModule`. However, the `XRUIInputModule` currently does not support sending UI Toolkit events from the Event System on behalf of the XRUIInputModule. Instead, `EventSystem.SetUITookitEventSystemOverride` can be called to bypass this default mechanism when it becomes the current/activated Input Module by the `EventSystem`. You can activate this function via the Unity Editor in the XR UI Input Module called **Bypass UI Toolkit Events**.

Added an optional bypass for UI Toolkit events that may cause incorrect events to get sent to UI Toolkit elements such as scroll views. Bug does not occur using Unity 2022.3.62f1 after editing Package Manifest to use XRI 2.6.4 then updating Starter Assets XRI package sample.