Add WebGPU Backend w/ Dawn Support (#3838)

src/mbgl/shaders/webgpu/heatmap.cpp

@@ -0,0 +1,18 @@
+#include <mbgl/shaders/webgpu/heatmap.hpp>
+#include <mbgl/shaders/shader_defines.hpp>
+#include <mbgl/shaders/heatmap_layer_ubo.hpp>
+
+namespace mbgl {
+namespace shaders {
+
+using HeatmapShaderSource = ShaderSource<BuiltIn::HeatmapShader, gfx::Backend::Type::WebGPU>;
+
+const std::array<AttributeInfo, 3> HeatmapShaderSource::attributes = {
+    AttributeInfo{0, gfx::AttributeDataType::Short2, idHeatmapPosVertexAttribute},
+    AttributeInfo{1, gfx::AttributeDataType::Float2, idHeatmapWeightVertexAttribute},
+    AttributeInfo{2, gfx::AttributeDataType::Float2, idHeatmapRadiusVertexAttribute},
+};
+const std::array<TextureInfo, 0> HeatmapShaderSource::textures = {};
+
+} // namespace shaders
+} // namespace mbgl