Refactor CppSignatureGroup to collect signatures as list. (#83667)
This makes it easier to add more signatures to the signature group,
as relevant logic which needs to run for each signature no longer
needs to be adjusted.
Signed-off-by: Edward Z. Yang <ezyang@fb.com>
Pull Request resolved: https://github.com/pytorch/pytorch/pull/83667
Approved by: https://github.com/larryliu0820, https://github.com/bdhirsh
