XRRenderState：inlineVerticalFieldOfView 属性
Limited availability
This feature is not Baseline because it does not work in some of the most widely-used browsers.
XRRenderState 接口的 inlineVerticalFieldOfView 只读属性返回 "inline" 会话的默认垂直视场，对于所有沉浸式会话则返回 null。