This patch changes how we deal with window control buttons on left
layouts. Previously, we looked to a pref that was only set on macos
but with this patch we use media queries to detect whether the system
is macOS or gtk-csd buttons use left-side layout.
To support old-style "override pref" this patch also introduces a
new custom pref userchrome.force-window-controls-on-left.enabled
which can be used e.g on Windows to move window controls to left side.
This logic is currently only supported in styles that use
window_control_placeholder_support.css
Using --toolbar-color allow the icons to show up if the selected theme
has light tabs but dark toolbar, and vice versa. In 95 there is no
separate #window-controls for fullscreen, and thus the titlebar-buttonbox-container
becomes last-child which we don't want to hide.
This way we can handle maximized windows not having the other drag space
like Firefox does normally. This patch additionally adds window control
width values for Win7 Win8 and linux
