Change "named_guard" in native_functions to "supports_named_tensor" (#26352)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/26352
"named_guard: P" is the same as "supports_named_tensor: !P".
Also changed the error message to be more understandable to users.
Test Plan:
- `TEST_NAMEDTENSOR=1 pytest test/test_namedtensor.py -v`
- [namedtensor ci]
Differential Revision: D17426234
Pulled By: zou3519
fbshipit-source-id: 4cab780e6e29e184e79cdd3690f41df9ebb2ecb5
