Allow using SVG images as project icon

[Calinou]

Since exporters will save their own icon, the target platforms don't have to support SVG to display the icon correctly.

In the future, we could consider supporting SVG favicons in the HTML5 export (whose support is quite good). This would require two things:

• If the project icon is in SVG format, modify the loading logic to copy the SVG icon from the project as favicon.svg and reference it in the HTML.
• When a SVG project icon is used, ignore requests to change the project icon from Godot itself, as it can only set a rasterized version of the icon. Perhaps this should be placed behind a project setting.

This closes #23068.

Preview

[akien-mga]

Since exporters will save their own icon, the target platforms don't have to support SVG to display the icon correctly.

I think at least Android uses the project icon by default, so this should likely be tested to confirm that it works.

[akien-mga]

Thanks!

[Riteo]

May I suggest to include this small tweak also into 3.2.4, if it's possible? It should be pretty easy to port(one small change into main.cpp) and shouldn't break anything.

[akien-mga]

Cherry-picked for 3.2.4.