Improve validator module behavior if Z3 is not installed. (#105168)
Fixes: #105143
In summary, the changes are:
- Check if Z3 is installed when the module is loaded
- Naming consistently as "translation validation" (not "validator")
- Skipping tests if Z3 is not installed
Pull Request resolved: https://github.com/pytorch/pytorch/pull/105168
Approved by: https://github.com/ezyang
