Keeps content whose colours are baked in at render time (bitmaps, SVG, highlighted runs)
in sync with the application theme. Standard controls follow theme changes on their own
through DynamicResource; this covers content that must be rebuilt instead.
public static class ThemeTracking
kind:method, kind:property, kind:ctor. Press Esc to clear.ReapplyOnThemeChange(StyledElement, Action)Calls apply whenever element is in a visual tree and the application theme differs from the one in effect when the content was last built: on a theme switch while attached, and on attach after a switch that happened while detached. While the element is hidden (it or an ancestor has Avalonia.Visual.IsVisible off, as with a viewer on an inactive tab), the rebuild waits until it is shown again. The caller builds the initial content itself; apply is not called here.