Add a warning if `WindowDescriptor` is inserted after the render plugin

[nicopap]

How can Bevy's documentation be improved?

To set the present_mode (aka vsync) of the bevy app, it is required that the WindowDescriptor resource be inserted before the insertion of the core bevy rendering plugin, so that it's possible to set the present mode when initializing rendering-related resources.

It is easy to mistakenly add the WindowDescriptor after the default bevy plugins. And there is absolutely no feedback telling user that they are "holding it wrong," resulting in difficult-to-understand unexpected behavior.

There should be a check on whether WindowDescriptor was inserted/updated after its useful insertion time and print a warning, explaining what problems this entails and how to fix the issue (adding the resource before the rendering plugin).

[IceSentry]

This PR would solve this more generally instead of being WindowDescriptor specific #2988