Improved texture loading (#3315)

* rework loading around `Arc<Loaders>`

* use `Bytes` instead of splitting api

* remove unwraps in `texture_handle`

* make `FileLoader` optional under `file` feature

* hide http load error stack trace from UI

* implement image fit

* support more image sources

* center spinner if we know size ahead of time

* allocate final size for spinner

* improve image format guessing

* remove `ui.image`, `Image`, add `RawImage`

* deprecate `RetainedImage`

* `image2` -> `image`

* add viewer example

* update `examples/image` + remove `svg` and `download_image` exapmles

* fix lints and tests

* fix doc link

* add image controls to `images` example

* add more `From` str-like types

* add api to forget all images

* fix max size

* do not scale original size unless necessary

* fix doc link

* add more docs for `Image` and `RawImage`

* make paint_at `pub`

* update `ImageButton` to use new `Image` API

* fix double rendering

* `SizeHint::Original` -> `Scale` + remove `Option` wrapper

* Update crates/egui/src/load.rs

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

* remove special `None` value for `forget`

* Update crates/egui/src/load.rs

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

* add more examples to `ui.image` + add `include_image` macro

* Update crates/egui/src/ui.rs

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

* update `menu_image_button` to use `ImageSource`

* `OrderedFloat::get` -> `into_inner`

* derive `Eq` on `SizedTexture`

* add `id` to loaders + `is_installed` check

* move `images` to demo + simplify `images` example

* log trace when installing loaders

* fix lint

* fix doc link

* add more documentation

* more `egui_extras::loaders` docs

* Update examples/images/src/main.rs

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

* update `images` example screenshots + readme

* remove unused `rfd` from `images` example

* Update crates/egui_extras/src/loaders/ehttp_loader.rs

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

* add `must_use` on `Image` and `RawImage`

* document `loaders::install` multiple call safety

* Update crates/egui_extras/Cargo.toml

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

* reshuffle `is_loader_installed`

* make `include_image` produce `ImageSource` + update docs

* update `include_image` docs

* remove `None` mentions from loader `forget`

* inline `From` texture id + size for `SizedTexture`

* add warning about statically known path

* change image load error + use in image button

* add `.size()` to `Image`

* Update crates/egui_demo_app/Cargo.toml

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

* add explanations to image viewer ui

---------

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

crates/egui_demo_app/src/wrap_app.rs

@@ -82,6 +82,8 @@ enum Anchor {
     EasyMarkEditor,
     #[cfg(feature = "http")]
     Http,
+    #[cfg(feature = "image_viewer")]
+    ImageViewer,
     Clock,
     #[cfg(any(feature = "glow", feature = "wgpu"))]
     Custom3d,
@@ -142,6 +144,8 @@ pub struct State {
     easy_mark_editor: EasyMarkApp,
     #[cfg(feature = "http")]
     http: crate::apps::HttpApp,
+    #[cfg(feature = "image_viewer")]
+    image_viewer: crate::apps::ImageViewer,
     clock: FractalClockApp,
     color_test: ColorTestApp,
 
@@ -161,6 +165,9 @@ pub struct WrapApp {
 
 impl WrapApp {
     pub fn new(_cc: &eframe::CreationContext<'_>) -> Self {
+        #[cfg(feature = "image_viewer")]
+        egui_extras::loaders::install(&_cc.egui_ctx);
+
         #[allow(unused_mut)]
         let mut slf = Self {
             state: State::default(),
@@ -204,6 +211,12 @@ impl WrapApp {
                 Anchor::Clock,
                 &mut self.state.clock as &mut dyn eframe::App,
             ),
+            #[cfg(feature = "image_viewer")]
+            (
+                "🖼️ Image Viewer",
+                Anchor::ImageViewer,
+                &mut self.state.image_viewer as &mut dyn eframe::App,
+            ),
         ];
 
         #[cfg(any(feature = "glow", feature = "wgpu"))]