add block material shaders

- 'shader' property of block materials: shaders/materials/<name>.glslv, .glslf with material_vertex / material_fragment hooks and #param uniforms
- material shaders code is included into main, translucent and shadows programs through generated headers, no extra draw calls
- chunk vertex normal.w byte replaced with 'flags': bit 7 - emission flag, bits 0-6 - material shader index (vertex format size is not changed)
- doc/*/block-materials.md

src/graphics/render/MaterialShaders.hpp

@@ -0,0 +1,39 @@
+#pragma once
+
+#include <string>
+
+#include "data/dv_fwd.hpp"
+
+class Content;
+class Shader;
+class ResPaths;
+class GLSLExtension;
+
+/// @brief Material shaders (shaders/materials/<name>.glslv, .glslf) are
+/// included into the world shaders (main, translucent, shadows, entity)
+namespace material_shaders {
+    inline constexpr const char* VERTEX_HEADER = "__materials_vertex__";
+    inline constexpr const char* FRAGMENT_HEADER = "__materials_fragment__";
+
+    /// @brief Generate the world shaders headers from the material shaders.
+    /// Must be called before the world shaders (re)compilation.
+    /// @param content loaded content (nullable)
+    void build_headers(
+        GLSLExtension& preprocessor,
+        const ResPaths& paths,
+        const Content* content
+    );
+
+    /// @brief Upload the material shaders params to the shader
+    /// if changed since the previous call for this shader program
+    void setup_shader(Shader& shader);
+
+    /// @brief Set the material shader params values ('param' directives)
+    /// @param material material name (pack:name)
+    /// @throws std::runtime_error if material or param does not exist
+    void set_params(const std::string& material, const dv::value& params);
+
+    /// @brief Get the material shader params current values
+    /// @return table of param name -> value or null if material has no shader
+    dv::value get_params(const std::string& material);
+}