Update base for Update on "[8/n][ET-VK] Support staging any 8-bit texture"

"bitw8" = bit width 8, which is equivalent to 8-bit. We use "bitw8" as the name since shader compilation disallows names starting with a digit.

Changes follow from #4485 to support `texture2d` and support `uint8`, respectively.

Differential Revision: [D63918659](https://our.internmc.facebook.com/intern/diff/D63918659/)

[ghstack-poisoned]

Author: jorgep31415