[tensorexpr] Add flag to fuse with unknown shapes (#44401)
Summary:
This flag simply allows users to get fusion groups that will *eventually* have shapes (such that `getOperation` is a valid).
This is useful for doing early analysis and compiling just in time.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/44401
Reviewed By: ZolotukhinM
Differential Revision: D23656140
Pulled By: bwasti
fbshipit-source-id: 9a26c202752399d1932ad7d69f21c88081ffc1e5
