Alters the FontMap of this FontMapping. This method is especially used to change the "Symbol" FontMapping after it has been registered with its default map. The custom configuration of this plugin might then change this map or replace it entirely.
If a config is applied to a FontMapping with "replace" mode,
a new map, based on the htmlEncodingMap will be created.
htmlEncodingMap is a minimum replacement map for custom mapping.
As we decode the HTML prior to replacement we need to ensure, that the
encoded characters are restored.
A FontMapping defines a strategy on how to map characters of a given font-family to their alternative representation.
A FontMapping must be provided with a corresponding map that defines the representation mapping for the font's characters. Please note, that a given map will always be extended with an htmlEncodingMap, a minimum replacement map for custom mappings.