UI Focus System improvements

[valaphee]

Objective

At the moment the position where a click has occurred has to be manually tracked.

Solution

This PR makes the process easier, by providing the position where the button has clicked, not changing while it is clicked (in contrast to RelativeCursorPosition). It also improves the understand-ability/readability of the ui_focus_system by getting rid of the partial-read iterator, replacing it with easy-readable if statements.

Changelog

• added Vec2(position of the click) to Interaction::Clicked

Migration Guide

• replace *interaction == Interaction::Clicked with matches!(*interaction, Interaction::Clicked(_))

[valaphee]

It also might be a good idea to use non-normalized positions in the RelativeCursorPosition component, or normalized positions in the Interaction::Clicked