blender: Build with Draco support (#245535)

See https://github.com/NixOS/nixpkgs/issues/217921

Blender sets WITH_DRACO=OFF if WITH_PYTHON_INSTALL=OFF, however that’s
not totally necessary. Removing that forced-set then builds with
WITH_DRACO=ON, however Blender fails to launch because this creates
e.g. `share/blender/3.6/python`, and Blender then sets this as Python’s
home dir, so Python fails to init since it expects Python core to be
there (and it’s not). I couldn’t figure out how Blender sets Python’s
home dir, and explicitly setting PYTHONHOME in the env didn’t have any
effect. So instead just rename that dir to python-ext to avoid this
behavior. All that is left then is to adjust where Blender is looking
for the Draco lib.

This functionality may be verified by:

1. Visiting File → Export → glTF 2.0
2. In the right side panel (press the gear icon in top-right if not
   visible), expanding “Data”
3. Enabling “Compression”
4. Press “Export glTF 2.0”
5. Verify:
   - Blender stdout+stderr shows “Draco mesh compression is available”
   - no error or warning message
   - exported file exists

0 files changed, 0 insertions, 0 deletions