Add vmap support for slogdet; fix regression from functorch 0.2.1 (#86815)
This PR adds vmap support for slogdet -- slogdet just decomposes into
linalg.slogdet.
This fixes a regression from functorch 0.2.1 (slogdet had a batching
rule then, and doesn't anymore). We didn't catch the regression because
it seems like slogdet doesn't have an OpInfo (I'm not sure if it had one
before).
Test Plan:
- new one-off test.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/86815
Approved by: https://github.com/samdow
