Adds `Marginf` to fill the previous niche.
This is all in a pursuit to shrink the sizes of often-used structs, to
improve performance (less cache misses, less memcpy:s, etc).
* On the path towards https://github.com/emilk/egui/issues/4019
* Closes https://github.com/emilk/egui/issues/3444
* Closes https://github.com/emilk/egui/issues/865
On a touch screen, if you press down on a widget and hold for 0.6
seconds (`MAX_CLICK_DURATION`), it will now trigger a secondary click,
i.e. `Response::secondary_clicked` will be `true`. This means you can
now open context menus on touch screens.
# What's New
* eframe: Added `App::raw_input_hook` allows for the manipulation or
filtering of raw input events
A filter applied to raw input before [`Self::update`]
This allows for the manipulation or filtering of input events before
they are processed by egui.
This can be used to exclude specific keyboard shortcuts, mouse events,
etc.
Additionally, it can be used to add custom keyboard or mouse events
generated by a virtual keyboard.
* examples: Added an example to demonstrates how to implement a custom
virtual keyboard.
[eframe-custom-keypad.webm](https://github.com/emilk/egui/assets/1274171/a9dc8e34-2c35-4172-b7ef-41010b794fb8)
Emil Ernerfeldt
Varphone Wong