love.graphics: move more platform-independent code out of the opengl backend

--HG--
branch : minor

src/modules/graphics/Text.h

@@ -63,6 +63,9 @@ public:
 	 **/
 	int getHeight(int index = 0) const;
 
+	// Implements Drawable.
+	void draw(love::graphics::Graphics *gfx, const Matrix4 &m) override;
+
 protected:
 
 	struct TextData
@@ -80,6 +83,8 @@ protected:
 	void regenerateVertices();
 	void addTextData(const TextData &s);
 
+	virtual void drawInternal(const std::vector<Font::DrawCommand> &commands) const = 0;
+
 	StrongRef<Font> font;
 	Buffer *vbo;
 	QuadIndices quadIndices;