LibGL: Implement `GL_SAMPLES`, `GL_SAMPLE_BUFFERS` context parameters

We do not support multisampling right now, so we return constant values
that indicate this.

Userland/Libraries/LibGL/ContextParameter.cpp

@@ -110,6 +110,10 @@ Optional<ContextParameter> GLContext::get_context_parameter(GLenum name)
         return ContextParameter { .type = GL_BOOL, .is_capability = true, .value = { .boolean_value = m_depth_offset_enabled } };
     case GL_RED_BITS:
         return ContextParameter { .type = GL_INT, .value = { .integer_value = sizeof(u8) * 8 } };
+    case GL_SAMPLE_BUFFERS:
+        return ContextParameter { .type = GL_INT, .value = { .integer_value = 0 } };
+    case GL_SAMPLES:
+        return ContextParameter { .type = GL_INT, .value = { .integer_value = 1 } };
     case GL_SCISSOR_BOX: {
         auto scissor_box = m_rasterizer->options().scissor_box;
         return ContextParameter {

Userland/Libraries/LibGL/GL/gl.h

@@ -146,6 +146,8 @@ extern "C" {
 #define GL_MAP2_VERTEX_4 0x0DB8
 #define GL_NORMAL_ARRAY 0x8075
 #define GL_NORMAL_ARRAY_TYPE 0x807E
+#define GL_SAMPLE_BUFFERS 0x80A8
+#define GL_SAMPLES 0x80A9
 #define GL_MAX_TEXTURE_LOD_BIAS 0x84FD
 
 // Blend factors