Add ImageFormatSetting::Guess to image loader

[Azorlogh]

Objective

• Allow using image assets that don't have an extensions and whose format is unknown. This is useful for loading images from arbitrary HTTP URLs.

Solution

• This PR adds a new variant to ImageFormatSetting called Guess. The loader will use image::guess_format to deduce the format based on the content of the file.

Testing

• I locally removed the extension of bevy_bird_dark, and ran a modified version of the sprite example:

//! Displays a single [`Sprite`], created from an image.

use bevy::{
    prelude::*,
    render::texture::{ImageFormatSetting, ImageLoaderSettings},
};

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_systems(Startup, setup)
        .run();
}

fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
    commands.spawn(Camera2dBundle::default());
    commands.spawn(SpriteBundle {
        texture: asset_server
            .load_with_settings("branding/bevy_bird_dark", |s: &mut ImageLoaderSettings| {
                s.format = ImageFormatSetting::Guess
            }),
        ..default()
    });
}

Changelog

Added

ImageFormatSetting::Guess to automatically guess the format of an image asset from its content.

[Azorlogh]

Note: when loading images without extension, a warning gets logged to the console:
Multiple AssetLoaders found for Asset: Some(TypeId { t: (6046691006513703432, 8515571476300803229) }); Path: Some(branding/bevy_bird_dark); Extension: None
However this warning was already present on main when using ImageFormatSetting::Format. I believe it's because of HdrTextureLoader. ImageLoader is always registered after HdrTextureLoader, so it should take precedence over it.

[mockersf]

random ci failure, trying to retrigger it

[alice-i-cecile]

The first commit from this PR was taken from 6b3ffac by @robtfm. @Azorlogh, in the future, either add Co-authored by: to your Git commit message or base your branch directly on old work to make sure credit is preserved properly.

[Azorlogh]

The first commit from this PR was taken from 6b3ffac by @robtfm. @Azorlogh, in the future, either add Co-authored by: to your Git commit message or base your branch directly on old work to make sure credit is preserved properly.

Oh wow. I don't recall seeing that PR/commit at all 😲 I just wrote this for internal use in my app (as an ugly wrapper around ImageLoader) and then up-streamed it here after some cleanup. I didn't realize there was already another one opened.
I should have checked for duplicates, my apologies.

[alice-i-cecile]

No worries! This change was pretty mechanical: very reasonable that the first step looked extremely similar <3