[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, 4 insertions, 2 deletions

diff --git a/test/tile/vector_tile.test.cpp b/test/tile/vector_tile.test.cpp
index 2fe2586ec2..49fdcbd9f8 100644
--- a/test/tile/vector_tile.test.cpp
+++ b/test/tile/vector_tile.test.cpp
@@ -61,9 +61,11 @@ TEST(VectorTile, Issue7615) {
     style::SymbolLayer symbolLayer("symbol", "source");
     auto symbolBucket = std::make_shared<SymbolBucket>(
         style::SymbolLayoutProperties::Evaluated(),
-        std::unordered_map<std::string, style::SymbolPaintProperties::Evaluated>(),
+        std::unordered_map<
+            std::string,
+            std::pair<style::IconPaintProperties::Evaluated, style::TextPaintProperties::Evaluated>>(),
         0.0f, false, false);
-
+    
     // Simulate placement of a symbol layer.
     tile.onPlacement(GeometryTile::PlacementResult {
         {{