Add user defined style properties

[Zoxc]

This adds user defined style properties and uses it for a couple of scroll properties as an example.

Properties are defined like:

prop!(pub scroll_bar_color: Color { inherited: true } = Color::rgba8(0, 0, 0, 120));
prop!(pub bg_active_color: Color { inherited: true } = Color::rgba8(0, 0, 0, 30));

They can be changed by Style::set:

view.style(|s| s.set(bg_active_color, Color::rgba8(166, 166, 166, 40)))

I've also added a macro to define an extractor which can be used in views to store relevant styles in an efficient way for later use. The scroll view makes use of it:

prop_extracter! {
    Extracter {
        scroll_bar_color,
        bg_active_color: OptionReader<bg_active_color>,
    }
}

[codecov]

Codecov Report

Merging #125 (abd3ce4) into main (646a1fb) will decrease coverage by 0.03%.
The diff coverage is 2.11%.

@@           Coverage Diff            @@
##            main    #125      +/-   ##
========================================
- Coverage   3.11%   3.09%   -0.03%     
========================================
  Files         54      54              
  Lines       9888    9961      +73     
========================================
  Hits         308     308              
- Misses      9580    9653      +73     

Files	Coverage Δ
src/window_handle.rs	0.00% <ø> (ø)
src/views/scroll.rs	0.00% <0.00%> (ø)
src/view.rs	0.00% <0.00%> (ø)
src/context.rs	0.00% <0.00%> (ø)
src/style.rs	18.04% <3.37%> (-2.25%)	⬇️

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more