LibGL+LibSoftGPU: Add GPU side shader infrastructure

This adds a shader class to LibSoftGPU and makes use of it when linking
GLSL program in LibGL. Also adds actual rendering code to the shader
tests.

Userland/Libraries/LibGL/Shaders/Program.cpp

@@ -48,7 +48,7 @@ ErrorOr<void> Program::attach_shader(Shader& shader)
     return {};
 }
 
-ErrorOr<void> Program::link()
+ErrorOr<void> Program::link(GPU::Device& device)
 {
     m_info_log = TRY(String::from_utf8(""sv));
 
@@ -86,6 +86,9 @@ ErrorOr<void> Program::link()
 
     m_linked_fragment_shader = linked_fragment_shader_or_error.release_value();
 
+    m_gpu_vertex_shader = TRY(device.create_shader({}));
+    m_gpu_fragment_shader = TRY(device.create_shader({}));
+
     m_link_status = true;
     return {};
 }