Miscellaneous fixes for Vulkan docs (#5972)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/5972

## Context

Implement various fixes to Vulkan delegate while performing QA for Vulkan docs. I elected to package everything into this one diff so that it is easy to cherrypick into the 0.4 release.

imported-using-ghimport

Test Plan: Imported from OSS

Reviewed By: jorgep31415

Differential Revision: D64022818

Pulled By: SS-JIA

fbshipit-source-id: 35782970e9db1ab33154ccbae2e10c77d911c041