Label text will now be centered, right-aligned and/or
justified based on the layout.
Galleys are no longer always pivoted in the left top corner,
so now have a Rect rather than just a size.
* First pass (missing rendering the bar)
* Render horizontal bars, and change Window scroll API
* emath: add impl Index + IndexMut for Align2
* Scrolling: fix subtle sizing bugs
* Add horizontal scrolling to color test
* try to wrap content before showing scrollbars, + add auto-shrink option
* Add hscroll to the misc demo window
* Fix for putting wrapping labels in an infinitely wide layout
* Add a egui_asserts to protect against nans in the layout engine
* Add line about horizontal scrolling to changelog
* Add example to docs of ScrollArea
* code cleanup
* Allow using the layout cursor to restrict available area
* Avoid id clashes when putting panels inside a Ui
* Panels: Propagate height/width range to inner Ui
* Allow easy placement of panels inside of Ui:s
* demo: simplify Windows with Panels demo
