Managed texture loading (#3297)

* add types from proposal

* add load methods on `egui::Context`

* implement loaders from proposal in `egui_extras`

* impl `From<Vec2>` for `SizeHint`

* re-export `SizeHint` from `egui` root

* rework `svg` example to use new managed `Image`

* split loaders into separate files + add logging

* add `log_trace`

* clean up `RetainedImage` from `svg` example

* refactor ehttp loader response to bytes mapping

* remove spammy trace

* load images even without extension

* fix lints

* remove unused imports

* use `Image2` in `download_image`

* use `visuals.error_fg_color` in `Image2` error state

* update lockfile

* use `Arc<ColorImage>` in `ImageData` + add `forget` API

* add `ui.image2`

* add byte size query api

* use iterators to sum loader byte sizes

* add static image loading

* use static image in `svg` example

* small refactor of `Image2::ui` texture loading code

* add `ImageFit` to size images properly

* remove println calls

* add bad image load to `download_image` example

* add loader file extension support tests

* fix lint errors in `loaders`

* remove unused `poll-promise` dependency

* add some docs to `Image2`

* add some docs to `egui_extras::loaders::install`

* explain `loaders::install` in examples

* fix lint

* upgrade `ehttp` to `0.3` for some crates

* Remove some unused dependencies

* Remove unnecessary context clone

* Turn on the `log` create feature of egui_extras in all examples

* rename `forget` and document it

* derive `Debug` on `SizeHint`

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

* round when converting SizeHint from vec2

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

* add `load` module docs

* docstring `add_loader` methods

* expose + document `load_include_bytes`

* cache texture handles in `DefaultTextureLoader`

* add `image2` doctest + further document `Image2`

* use `Default` for default `Image2` options

* update `image2` doc comment

* mention immediate-mode safety

* more fit calculation into inherent impl

* add hover text on spinner

* add `all-loaders` feature

* clarify `egui_extras::loaders::install` behavior

* explain how to enable image formats

* properly format `uri`

* use `thread::Builder` instead of `spawn`

* use eq op instead of `matches`

* inline `From<Arc<ColorImage>>` for `ImageData`

* allow non-`'static` bytes + `forget` in `DefaultTextureLoader`

* sort features

* change `ehttp` feature to `http`

* update `Image2` docs

* refactor loader cache type

---------

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

crates/egui_extras/Cargo.toml

@@ -26,12 +26,18 @@ all-features = true
 [features]
 default = []
 
+## Shorthand for enabling `svg`, `image`, and `ehttp`.
+all-loaders = ["svg", "image", "http"]
+
 ## Enable [`DatePickerButton`] widget.
 datepicker = ["chrono"]
 
 ## Log warnings using [`log`](https://docs.rs/log) crate.
 log = ["dep:log", "egui/log"]
 
+## Add support for loading images via HTTP.
+http = ["dep:ehttp"]
+
 ## Enable profiling with the [`puffin`](https://docs.rs/puffin) crate.
 ##
 ## Only enabled on native, because of the low resolution (1ms) of clocks in browsers.
@@ -40,7 +46,6 @@ puffin = ["dep:puffin", "egui/puffin"]
 ## Support loading svg images.
 svg = ["resvg", "tiny-skia", "usvg"]
 
-
 [dependencies]
 egui = { version = "0.22.0", path = "../egui", default-features = false }
 
@@ -76,3 +81,6 @@ puffin = { version = "0.16", optional = true }
 resvg = { version = "0.28", optional = true, default-features = false }
 tiny-skia = { version = "0.8", optional = true, default-features = false } # must be updated in lock-step with resvg
 usvg = { version = "0.28", optional = true, default-features = false }
+
+# http feature
+ehttp = { version = "0.3.0", optional = true, default-features = false }