[SYCL] Cherry-pick "Switch to use plain array in `sycl::vec` in more cases" to sycl-rel-6_0_0#17695

uditagarwal97 wants to merge 1 commit intointel:sycl-rel-6_0_0intel/llvm:sycl-rel-6_0_0from

AlexeySachkov:private/asachkov/cherry-pick-vec-fixAlexeySachkov/llvm:private/asachkov/cherry-pick-vec-fixCopy head branch name to clipboard