feat: configure whether or not to lazy load

I'm using an `ion-icon` in a dropdown interface, where a user has to click an element to show the dropdown's content. Because of how ionicons is implemented, the icons inside the dropdown are not loaded instantly because the request is performed when it is visible to the user.

This, of course, is not ideal, as it shows a flicker while the icons are not downloaded. Just like what happens when you set a `background-image` to an element in its `:hover` state.

Is there any way to force the load of invisible icons?

该 issue 提到了 ion-icon 及其由可见性触发的 lazy loading，但没有提供可供开始的文件或测试。跟踪在图标变为可见时请求图标的实现，然后确定配置应如何允许不可见的图标立即加载，并验证 dropdown 图标不再闪烁。

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