Python: gpu module: add new submodules and types

This commit extends the gpu python API with:
```
gpu.types.Buffer         #"__init__", "to_list"
gpu.types.GPUTexture     #"__init__", "clear", "read", "format"
gpu.types.GPUFrameBuffer #"__init__", "bind", "clear", "is_bound", "viewport", ("__enter__",  "__exit__" with "GPUFrameBufferStackContext")
gpu.types.GPUUniformBuf  #"__init__", "update"
gpu.state                #"blend_set",  "blend_get",  "depth_test_set",  "depth_test_get",  "depth_mask_set",  "depth_mask_get",  "viewport_set",  "viewport_get",  "line_width_set",  "line_width_get",  "point_size_set",  "color_mask_set",  "face_culling_set", "front_facing_set",  "program_point_size_set"
```

Add these methods to existing objects:
```
gpu.types.GPUShader  #"uniform_sample", "uniform_buffer"
```

Maniphest Tasks: T80481

Differential Revision: https://developer.blender.org/D8826

source/blender/python/gpu/gpu_py_offscreen.h

@@ -28,7 +28,6 @@ extern PyTypeObject BPyGPUOffScreen_Type;
 
 typedef struct BPyGPUOffScreen {
   PyObject_HEAD struct GPUOffScreen *ofs;
-  bool is_saved;
 } BPyGPUOffScreen;
 
 PyObject *BPyGPUOffScreen_CreatePyObject(struct GPUOffScreen *ofs) ATTR_NONNULL(1);