Add layer to the style persistently.
Note: This is an experimental API and is a subject to change.
Whenever a new style is being parsed and currently used style has persistent layers, an engine will try to do following:
keep the persistent layer at its relative position
keep the source used by a persistent layer
keep images added through addStyleImage method
In cases when a new style has the same layer, source or image resource, style's resources would be used instead and MapLoadingError event will be emitted.