This adds wrapper classes that make it easier to use GPU objects in C++.

Motivations:

• Easier handling of GPU objects.
• EEVEE rewrite already makes use of similar wrappers.
• There is the ongoing effort to use more C++ in the codebase and lans to port more engines to it.
• The shader code refactor will make use of many UBOs with shared struct declaration. This helps managing them.
• Safer handling of TextureFromPool which can't be bound as normal texture (only texture ref) and can be better tracked in the future.

Considerations:

• I chose the blender::draw namespace because blender::gpu already has private classes (i.e: gpu::Texture).
• Theses are wrappers that manage a GPU object internally. They might be confused with actual Texture. However, the name TextureWrapper is a bit too much verbose in my opinion. I'm open to suggestion about better name.