This commit adds a new API tha allow to replace the bgl API in the exemples on:
https://docs.blender.org/api/current/gpu.html
**Overview (New API):**
```
gpu.state: active_framebuffer_get
GPUFramebuffer: read_color
GPUOffscreen: texture_color
```
Reviewed By: brecht
Differential Revision: https://developer.blender.org/D11031