[vulkan] Use aliases when retrieving from packed/unpacked lists in OpContexts (#83526)
Instead of retrieving elements of pack/unpacked lists using raw indices, this diff introduces aliases which improve code readability and guard against future errors.
Differential Revision: [D38748293](https://our.internmc.facebook.com/intern/diff/D38748293/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/83526
Approved by: https://github.com/manuelcandales
