[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, 31 insertions, 13 deletions

diff --git a/src/mbgl/style/layers/symbol_layer_impl.hpp b/src/mbgl/style/layers/symbol_layer_impl.hpp
index c00c2b0bba..1e9f05e4c7 100644
--- a/src/mbgl/style/layers/symbol_layer_impl.hpp
+++ b/src/mbgl/style/layers/symbol_layer_impl.hpp
@@ -1,5 +1,6 @@
 #pragma once
 
+#include <mbgl/util/variant.hpp>
 #include <mbgl/style/layer_impl.hpp>
 #include <mbgl/style/layers/symbol_layer.hpp>
 #include <mbgl/style/layers/symbol_layer_properties.hpp>
@@ -10,6 +11,30 @@ class SpriteAtlas;
 class SymbolLayout;
 
 namespace style {
+    
+
+// {icon,text}-specific paint-property packs for use in the symbol Programs.
+// Since each program deals either with icons or text, using a smaller property set
+// lets us avoid unnecessarily binding attributes for properties the program wouldn't use.
+class IconPaintProperties : public PaintProperties<
+    IconOpacity,
+    IconColor,
+    IconHaloColor,
+    IconHaloWidth,
+    IconHaloBlur,
+    IconTranslate,
+    IconTranslateAnchor
+> {};
+    
+class TextPaintProperties : public PaintProperties<
+    TextOpacity,
+    TextColor,
+    TextHaloColor,
+    TextHaloWidth,
+    TextHaloBlur,
+    TextTranslate,
+    TextTranslateAnchor
+> {};
 
 // Repackaging evaluated values from SymbolLayoutProperties + SymbolPaintProperties
 // for genericity over icons vs. text.
@@ -21,24 +46,14 @@ public:
     float layoutSize;
 
     // Paint
-    float opacity;
-    Color color;
-    Color haloColor;
-    float haloWidth;
-    float haloBlur;
     std::array<float, 2> translate;
     TranslateAnchorType translateAnchor;
     float paintSize;
 
     float sdfScale;   // Constant (1.0 or 24.0)
-
-    bool hasHalo() const {
-        return haloColor.a > 0.0f && haloWidth > 0.0f;
-    }
-
-    bool hasForeground() const {
-        return color.a > 0.0f;
-    }
+    
+    bool hasHalo;
+    bool hasFill;    
 };
 
 class SymbolLayer::Impl : public Layer::Impl {
@@ -54,6 +69,9 @@ public:
     std::unique_ptr<SymbolLayout> createLayout(const BucketParameters&, const std::vector<const Layer*>&,
                                                const GeometryTileLayer&) const;
 
+    IconPaintProperties::Evaluated iconPaintProperties() const;
+    TextPaintProperties::Evaluated textPaintProperties() const;
+    
     SymbolPropertyValues iconPropertyValues(const SymbolLayoutProperties::Evaluated&) const;
     SymbolPropertyValues textPropertyValues(const SymbolLayoutProperties::Evaluated&) const;