[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

scripts/generate-style-code.js

@@ -47,7 +47,20 @@ global.evaluatedType = function (property) {
 };
 
 function attributeType(property, type) {
-    const name = property.name.replace(type + '-', '').replace('-', '_');
+    const attributeNameExceptions = {
+      'text-opacity': 'opacity',
+      'icon-opacity': 'opacity',
+      'text-color': 'fill_color',
+      'icon-color': 'fill_color',
+      'text-halo-color': 'halo_color',
+      'icon-halo-color': 'halo_color',
+      'text-halo-blur': 'halo_blur',
+      'icon-halo-blur': 'halo_blur',
+      'text-halo-width': 'halo_width',
+      'icon-halo-width': 'halo_width'
+    }
+    const name = attributeNameExceptions[property.name] ||
+        property.name.replace(type + '-', '').replace(/-/g, '_');
     return `attributes::a_${name}${name === 'offset' ? '<1>' : ''}`;
 }