Allow overlapping interactive widgets (#2244)

* Turn off optimization for debug builds again

* Optimize rect_contains_pointer

* Fix for colorpicker: make popup immovable

* Area: interact first

* ScrollArea: do interaction first

* Window: shrink double-clickable area of titelbar

* Only the top-most (latest added) interactive widget gets `hovered=true`

* Add Frame::total_margin

* Update changelog

* Add debug-options to visualize what widgets cover which other widget

CHANGELOG.md

@@ -6,6 +6,7 @@ NOTE: [`epaint`](crates/epaint/CHANGELOG.md), [`eframe`](crates/eframe/CHANGELOG
 
 ## Unreleased
 * ⚠️ BREAKING: egui now expects integrations to do all color blending in gamma space ([#2071](https://github.com/emilk/egui/pull/2071)).
+* ⚠️ BREAKING: if you have overlapping interactive widgets, only the top widget (last added) will be interactive ([#2244](https://github.com/emilk/egui/pull/2244)).
 
 ### Added ⭐
 * Added helper functions for animating panels that collapse/expand ([#2190](https://github.com/emilk/egui/pull/2190)).
@@ -15,7 +16,7 @@ NOTE: [`epaint`](crates/epaint/CHANGELOG.md), [`eframe`](crates/eframe/CHANGELOG
 * Texture loading now takes a `TexureOptions` with minification and magnification filters ([#2224](https://github.com/emilk/egui/pull/2224)).
 * Added `Key::Minus` and `Key::Equals` ([#2239](https://github.com/emilk/egui/pull/2239)).
 * Added `egui::gui_zoom` module with helpers for scaling the whole GUI of an app ([#2239](https://github.com/emilk/egui/pull/2239)).
-* Implemented `Debug` for `egui::Context` ([#2248](https://github.com/emilk/egui/pull/2248)).
+* You can now put one interactive widget on top of another, and only one will get interaction at a time ([#2244](https://github.com/emilk/egui/pull/2244)).
 
 ### Fixed 🐛
 * ⚠️ BREAKING: Fix text being too small ([#2069](https://github.com/emilk/egui/pull/2069)).