[core] Implement Expression::serialize()

Issue #10714
- Each expression stores its operator as a string, and default serialization is [operator, serialize(child1), ...]
- Custom implementations of `serialize` for Expression types that don't follow the pattern
- expression::Value -> mbgl::Value converter
- node_expression bindings to expose `serialize`

1 files changed, 1 insertions, 0 deletions

diff --git a/include/mbgl/style/expression/case.hpp b/include/mbgl/style/expression/case.hpp
index e61a55fc6d..667ca53712 100644
--- a/include/mbgl/style/expression/case.hpp
+++ b/include/mbgl/style/expression/case.hpp
@@ -28,6 +28,7 @@ public:
 
     std::vector<optional<Value>> possibleOutputs() const override;
 
+    std::string getOperator() const override { return "case"; }
 private:
     std::vector<Branch> branches;
     std::unique_ptr<Expression> otherwise;