[vulkan] Remove dependencies from op/ in vTensor and move it to higher level namespace (#91023)
Small refactor to remove any code used by vTensor under the `op/` folder to appropriate locations in the `api/` folder. Also remove vTensor from the `ops` namespace, it now resides in the higher level `at::native::vulkan` namespace which will also be used for the Graph data structures in the future.
This is the last step required for vTensor to be able to moved to the api folder.
Differential Revision: [D42052680](https://our.internmc.facebook.com/intern/diff/D42052680/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/91023
Approved by: https://github.com/salilsdesai
