public static void registerFontFamilyLoader( String family, Runnable loader ) {
		if( loadersMap == null )
			loadersMap = new HashMap<>();
		loadersMap.put( family, loader );
	}
Registers a font family for lazy loading via {@link #loadFontFamily(String)}.
<p>
The given runnable is invoked when the given font family should be loaded.
The runnable should invoke {@link #installFont(URL)} to load and register font(s)
for the family.
A family may consist of up to four font files for the supported font styles:
regular (plain), italic, bold and bold-italic.
flatlaf-core/src/main/java/com/formdev/flatlaf/util/FontUtils.java