Pass image URI:s unmolested to egui

[emilk]

We shouldn't be adding file:// prefixes to users URI:s for them.

If a user does this:

egui_ctx.include_bytes("bytes://image.png", include_bytes!("image.png"));

they should be able to put ![](bytes://image.png) in their markdown and have it work imho.

Of course, this change means users need to explicitly say file:// to indicate that the image should be loaded from a file at runtime. In this case, I think explicit is better than implicit though.

[lampsitter]

That's unfortunate. Would it be possible instead to check if the uri does not have a foo:// prefix and only insert file:// upon such scenarios? Or is that too crude? Specifying file:// everytime seems tedious.

[lampsitter]

I'd rather have an option to disable the auto insert of file://, so that it can be left up to the user what the prefer

[emilk]

What about this?

678803d