Adwaita: Fix fine-tune mode for scales with marks

I couldn't apply !612 (merged) to master, related code is different in gtk4.

This is how fine-tune mode looks in gtk4:

scales_marks1now

Removing old fine-tune marks code leads to this.

scales_marks2nofinetune

As you can see on previous screencast, widgets below scale are "jumping" up, i think it happens because of slider margin changes in fine tune mode, adding 3px margin to marks in fine-tune mode to compensate scale changes fixes it. Not sure if it is right. With margin:

scales_marks3finetunemargin

While entering fine-tune mode, marks placement changes, it is also related to slider margins changes (-10px in regular state -7px in fine-tune). I've changed slider margins, so through only grows in vertical directions on horizontal sliders (and only horizontal directions on vertical sliders). Final result:

scales_marks4slidermargin

I'm not exactly sure about all this changes and (especially!) commit message. Also, I've only tested horizontal scale with marks below.

Tested in gtk4-widget-factory from org.gnome.Platform//master (gnome-nightly repo) by running flatpak run --command=gtk4-widget-factory org.gnome.NautilusGtk4).

HC theme: code for scales with marks is the same as in gtk-3-24 branch, and taking into account #1450 (closed), I assume, there is no point to change something there.

Closes #1799 (closed)