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>

Cargo.lock

@@ -1083,16 +1083,6 @@ version = "1.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9ea835d29036a4087793836fa931b08837ad5e957da9e23886b29586fb9b6650"
 
-[[package]]
-name = "download_image"
-version = "0.1.0"
-dependencies = [
- "eframe",
- "egui_extras",
- "env_logger",
- "image",
-]
-
 [[package]]
 name = "dyn-clonable"
 version = "0.9.0"
@@ -1231,6 +1221,7 @@ dependencies = [
  "image",
  "log",
  "poll-promise",
+ "rfd",
  "serde",
  "wasm-bindgen",
  "wasm-bindgen-futures",
@@ -1264,6 +1255,7 @@ dependencies = [
  "ehttp",
  "image",
  "log",
+ "mime_guess",
  "puffin",
  "resvg",
  "serde",
@@ -2026,6 +2018,16 @@ dependencies = [
  "png",
 ]
 
+[[package]]
+name = "images"
+version = "0.1.0"
+dependencies = [
+ "eframe",
+ "egui_extras",
+ "env_logger",
+ "image",
+]
+
 [[package]]
 name = "imagesize"
 version = "0.10.1"
@@ -2310,6 +2312,22 @@ dependencies = [
  "paste",
 ]
 
+[[package]]
+name = "mime"
+version = "0.3.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6877bb514081ee2a7ff5ef9de3281f14a4dd4bceac4c09388074a6b5df8a139a"
+
+[[package]]
+name = "mime_guess"
+version = "2.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4192263c238a5f0d0c6bfd21f336a313a4ce1c450542449ca191bb657b4642ef"
+dependencies = [
+ "mime",
+ "unicase",
+]
+
 [[package]]
 name = "minimal-lexical"
 version = "0.2.1"
@@ -2998,16 +3016,6 @@ dependencies = [
  "usvg",
 ]
 
-[[package]]
-name = "retained_image"
-version = "0.1.0"
-dependencies = [
- "eframe",
- "egui_extras",
- "env_logger",
- "image",
-]
-
 [[package]]
 name = "rfd"
 version = "0.11.4"
@@ -3408,15 +3416,6 @@ version = "0.10.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "73473c0e59e6d5812c5dfe2a064a6444949f089e20eec9a2e5506596494e4623"
 
-[[package]]
-name = "svg"
-version = "0.1.0"
-dependencies = [
- "eframe",
- "egui_extras",
- "env_logger",
-]
-
 [[package]]
 name = "svgtypes"
 version = "0.8.2"
@@ -3747,6 +3746,15 @@ dependencies = [
  "winapi",
 ]
 
+[[package]]
+name = "unicase"
+version = "2.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f7d2d4dafb69621809a81864c9c1b864479e1235c0dd4e199924b9742439ed89"
+dependencies = [
+ "version_check",
+]
+
 [[package]]
 name = "unicode-bidi"
 version = "0.3.13"