explicit dynamic shapes maps namings (#172405) (#173017)
Summary:
- this map only used for backed.
var_to_val -> backed_var_to_val
- this map only used for real tensor prop
unbacked_var_to_val -> real_tensor_prop_unbacked_vals
X-link: https://github.com/pytorch/pytorch/pull/173017
Approved by: https://github.com/aorenste, https://github.com/bobrenjc93
Reviewed By: aorenste
Differential Revision: D91176254
fbshipit-source-id: 6b332548db5a0854fd0950639853c4e6e6a7522c