Update node bindings to support addImage with sdf images

[riastrad]

Currently if you build the node library from source on master and run render tests, the runtime-styling/image-add-sdf test will fail. This is because the node bindings don't currently parse the sdf attribute for the image when adding it.

To my untrained eye, this is the relevant part of the bindings:

mapbox-gl-native/platform/node/src/node_map.cpp

Lines 738 to 798 in 869ff70

	void NodeMap::AddImage(const Nan::FunctionCallbackInfo<v8::Value>& info) {
	using namespace mbgl::style;
	using namespace mbgl::style::conversion;
	auto nodeMap = Nan::ObjectWrap::Unwrap<NodeMap>(info.Holder());
	if (!nodeMap->map) return Nan::ThrowError(releasedMessage());
	if (info.Length() != 3) {
	return Nan::ThrowTypeError("Three arguments required");
	}
	if (!info[0]->IsString()) {
	return Nan::ThrowTypeError("First argument must be a string");
	}
	if (!info[1]->IsObject()) {
	return Nan::ThrowTypeError("Second argument must be an object");
	}
	if (!info[2]->IsObject()) {
	return Nan::ThrowTypeError("Third argument must be an object");
	}
	auto optionObject = Nan::To<v8::Object>(info[2]).ToLocalChecked();
	if (!Nan::Get(optionObject, Nan::New("height").ToLocalChecked()).ToLocalChecked()->IsUint32()) {
	return Nan::ThrowTypeError("height parameter required");
	}
	if (!Nan::Get(optionObject, Nan::New("width").ToLocalChecked()).ToLocalChecked()->IsUint32()) {
	return Nan::ThrowTypeError("width parameter required");
	}
	if (!Nan::Get(optionObject, Nan::New("pixelRatio").ToLocalChecked()).ToLocalChecked()->IsNumber()) {
	return Nan::ThrowTypeError("pixelRatio parameter required");
	}
	uint32_t imageHeight = Nan::Get(optionObject, Nan::New("height").ToLocalChecked()).ToLocalChecked()->Uint32Value();
	uint32_t imageWidth = Nan::Get(optionObject, Nan::New("width").ToLocalChecked()).ToLocalChecked()->Uint32Value();
	if (imageWidth > 1024 || imageHeight > 1024) {
	return Nan::ThrowTypeError("Max height and width is 1024");
	}
	float pixelRatio = Nan::Get(optionObject, Nan::New("pixelRatio").ToLocalChecked()).ToLocalChecked()->NumberValue();
	auto imageBuffer = Nan::To<v8::Object>(info[1]).ToLocalChecked()->ToObject();
	char * imageDataBuffer = node::Buffer::Data(imageBuffer);
	size_t imageLength = node::Buffer::Length(imageBuffer);
	if (imageLength != imageHeight * imageWidth * 4) {
	return Nan::ThrowTypeError("Image size does not match buffer size");
	}
	std::unique_ptr<uint8_t[]> data = std::make_unique<uint8_t[]>(imageLength);
	std::copy(imageDataBuffer, imageDataBuffer + imageLength, data.get());
	mbgl::UnassociatedImage cImage({ imageWidth, imageHeight}, std::move(data));
	mbgl::PremultipliedImage cPremultipliedImage = mbgl::util::premultiply(std::move(cImage));
	nodeMap->map->getStyle().addImage(std::make_unique<mbgl::style::Image>(*Nan::Utf8String(info[0]), std::move(cPremultipliedImage), pixelRatio));
	}

We should remedy this so that the node library can add SDF images without problems.

cc: @mapbox/gl-native @mapbox/maps-api