Add layer to the style persistently.
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
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.
The layer to be added to the style
the position that the current layer is added to