LibGL: Implement glTexParameter{i,f}

This currently only implements a subset of this function.
Namely setting wrap, mag and min modes for the GL_TETXURE_2D target.

Userland/Libraries/LibGL/Tex/Texture2D.h

@@ -42,6 +42,7 @@ public:
 
     GLenum internal_format() const { return m_internal_format; }
     Sampler2D const& sampler() const { return m_sampler; }
+    Sampler2D& sampler() { return m_sampler; }
 
 private:
     template<typename TCallback>