Gets or sets the file where the default operating-system font resolver keeps the index of the font files it has read, so a
later process finds installed fonts without reading their files again; null (the default) keeps no index and
writes nothing.
public string? SystemFontIndexPath { get; set; }
The file is created, with its directory, after the first font the operating system's fonts are asked for, and rewritten when more font files have been read. Font files added, removed or changed since are read again, so the index never changes which font is found. Engines with the same path share one resolver in the process. Applies only to the default resolver: one set with UseSystemFontResolver(IFontResolver?) keeps its own index (IndexPath).