Draw axis labels and ticks outside of plotting window (#2284)

* Always draw axis labels at plot borders

* Revert "Always draw axis labels at plot borders"

This reverts commit 9235e6603366d3b8a8189e2a5fc28c9780b7f54f.

* Add axis labels for plots

* First Draft of axis labels outside of plotting window

* plot: Tick placement of opposite axes and digit constraints

* plot: Axis label API

* plot: Update demo lib

* plot: resolve clippy warning

* Update changelog

* Remove default axis

* Fix clippy

* plot: Remove unused comments

* plot-axis: Rebase label opacity calculation on master

* plot: Resolve check.sh warnings

* plot-axis: Use 'into impl<WidgetText>' as axis label formatter

* plot-axis: Expose more conveniece functions to public API. Add axis labels to demo app

* plot-axes: Resolve ./scripts/check.sh warnings

* typo in comment

* Use `TAU` instead of the legacy `PI`

* Simpler generic syntax

* Use `Arc` to avoid some expensive clones

* Use `Margin` instead of a,b,c,d

* Add some vertical spacing

* De-duplicate color_from_contrast

* better naming

* Fix typos

* cnt -> num

* Axis are present by default, with empty names

* Add HPlacement and VPlacement

* Don't catch clicks and drags on axes

* Remove generics to minimize monomorphization code bloat

* Create helper function

* Remove changelog entry

* Simplify more

---------

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

crates/egui/src/widgets/mod.rs

@@ -38,6 +38,8 @@ pub use text_edit::{TextBuffer, TextEdit};
 ///
 /// [`Button`], [`Label`], [`Slider`], etc all implement the [`Widget`] trait.
 ///
+/// You only need to implement `Widget` if you care about being able to do `ui.add(your_widget);`.
+///
 /// Note that the widgets ([`Button`], [`TextEdit`] etc) are
 /// [builders](https://doc.rust-lang.org/1.0.0/style/ownership/builders.html),
 /// and not objects that hold state.