Make `rasterize_with_depth` and `transform_with_v_cam` accessable from the root drtk module

Summary:
Make `rasterize_with_depth` and `transform_with_v_cam`  accessible from the root drtk module as:

```
from drtk import rasterize_with_depth, transform_with_v_cam
```

instead of

```
from drtk.rasterize import rasterize_with_depth
from drtk.transform import transform_with_v_cam
```

This has greater importance for DGX and GitHub rather than prod, since because of how buck is setup, it still won't work.

Reviewed By: una-dinosauria

Differential Revision: D63440390

fbshipit-source-id: 7f6c8c16fb8ef5aa10bef3491fd59727f1000d0b

drtk/__init__.py

@@ -9,8 +9,8 @@ from .grid_scatter import grid_scatter, grid_scatter_ref  # noqa
 from .interpolate import interpolate, interpolate_ref  # noqa
 from .mipmap_grid_sample import mipmap_grid_sample, mipmap_grid_sample_ref  # noqa
 from .msi import msi  # noqa
-from .rasterize import rasterize  # noqa
+from .rasterize import rasterize, rasterize_with_depth  # noqa
 from .render import render, render_ref  # noqa
-from .transform import transform  # noqa
+from .transform import transform, transform_with_v_cam  # noqa
 
 __version__ = "0.1.0"  # noqa