[core] Implement data-driven styling for {text,icon}-{color,opacity,halo-color,halo-blur,halo-width} (#7939)

* Add symbol dds attributes and adapt style code generation

* Update to mapbox-gl-js/master

* Refactor SymbolFeature as a subclass of GeometryTileFeature

Prepares for enabling DDS on symbol paint properties by allowing the
SymbolFeatures, which we keep around after constructing SymbolLayout,
to be used in evaluating data-driven paint properties later in the
layout process.

* Draft approach for splitting icon/text paint properties

The `Program` types are set up to bind GL attributes to each of the
data-driven paint properties specified in the `PaintProperties` type
provided.  Since `SymbolPaintProperties` specifies both `Text*` and
`Icon*` properties, the symbolIcon, symbolIconSDF, and symbolGlyph
programs each attempt to bind roughly double the number of attributes
that they actually need.

This change addresses this by:
- Adding the more specific `IconPaintProperties` and `TextPaintProperties` types, which are subsets of the full `SymbolPaintProperties`.
- The symbol layer continues to use its `SymbolPaintProperties paint` member to track layer property state, but it provides helpers that construct objects of each the specific `{Icon,Text}PaintProperties::Evaluated` type, for use by the painter.
- The three symbol programs instantiate `Program<>` using the appropriate `{Icon,Text}PaintProperties` type.

* check in generated style code

* Populate paint buffers for symbol DDS properties

* Address first round of review comments

* Refactor VectorTile{Layer,Feature} to explicitly share data

* Update submodule

1 files changed, 5 insertions, 2 deletions

diff --git a/src/mbgl/layout/symbol_layout.hpp b/src/mbgl/layout/symbol_layout.hpp
index dbfdad22d9..491d0078da 100644
--- a/src/mbgl/layout/symbol_layout.hpp
+++ b/src/mbgl/layout/symbol_layout.hpp
@@ -5,6 +5,7 @@
 #include <mbgl/layout/symbol_feature.hpp>
 #include <mbgl/layout/symbol_instance.hpp>
 #include <mbgl/text/bidi.hpp>
+#include <mbgl/style/layers/symbol_layer_impl.hpp>
 
 #include <memory>
 #include <map>
@@ -51,10 +52,12 @@ public:
 
     State state = Pending;
 
-    std::unordered_map<std::string, style::SymbolPaintProperties::Evaluated> layerPaintProperties;
+    std::unordered_map<std::string,
+        std::pair<style::IconPaintProperties::Evaluated, style::TextPaintProperties::Evaluated>> layerPaintProperties;
 
 private:
-    void addFeature(const SymbolFeature&,
+    void addFeature(const size_t,
+                    const SymbolFeature&,
                     const std::pair<Shaping, Shaping>& shapedTextOrientations,
                     const PositionedIcon& shapedIcon,
                     const GlyphPositions& face);