Allow Naming of Symbol Layers for Multilayered Symbologies and Exporting the names to Vector Tiles

[Matthew_Muehlhauser]

When exporting vector tiles, layers that have a symbol that contains complex layering to create the symbol are converted by giving a unique ID to each layer of the symbol.

For example, a polygon with a border and a fill is exported with the border getting the id 0 and the fill id 1. If a user is trying to edit the vector tile style, they will see 0 and 1 and may not be able to tell from the naming what each is doing. 

This can be worked around a couple of ways, 1 is by duplicating the layer and making each layer one part of the symbol, which will be a pain to maintain. Or 2 is by editing the JSON of the style after exporting, which can be tedious unless it's automated.

For a potential solution, if the symbol layers were able to be named, then the names could be used instead of ids. This way they can be described for the vector tile output. This could also be helpful in general for maintaining complex symbologies as well.