Rename FeatureTable into Layer

[nyurik]

It seems the FeatureTable concept described in the spec is semantically identical to the MVT's Layer. If so, I think it would be better to use the same terminology to avoid confusion and to simplify adaption. Or does the featuretable has any additional semantic meaning?

[1ec5]

“Layer” is a familiar term, but it’s also a very overloaded term. I’m constantly struggling to distinguish between tile layers and style layers in conversation. (Look, they even rhyme when fully qualified!)

[kkaefer]

I think calling this "Layer" was a mistake in the original spec and it stems from the (invalid) assumption that each layer would only be rendered once. In the code, we have to use names like "SourceLayer" to distinguish it from the style layers.

[kkaefer]

Plus, "layer" doesn't actually describe the concept well. I think FeatureTable, FeatureCollection (like in GeoJSON)orFeautreset` would be better terms.