Vulkan: Fix `precise` vs `mat4(...)[index]` Bug: angleproject:374801303 Change-Id: I45550abe406aaaf4d2c5eb5d7d694b2b30ab8e4e Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5949528 Reviewed-by: mohan maiya <m.maiya@samsung.com> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Charlie Lao <cclao@google.com>