[M96-LTS] Vulkan: Update mCurrentElementArrayBuffersync based on dirty bit

M96 merge issues:
ContextVk.cpp:
ContextVk::setupIndexedDraw: vertexArrayVk/getVertexArray() isn't present in M96
ContextVk::syncState: M96 uses mVertexArray instead of vertexArrayVk
VertexArrayVk.cpp:
VertexArrayVk::updateCurrentElementArrayBuffer doesn't exist in M9
Created it and kept M96 logic for retrieving buffer/offset

The previous fix crrev.com/c/3513553 has run into corner case that
requires more follow up change crrev.com/c/3522565. But with that, there
is report that now we are hitting assertion in
handleDirtyGraphicsIndexBuffer(). This becomes a bit fragile This new
fix relies on the DIRTY_BIT_INDEX_BUFFER dirty bit and should be more
reliable as long as the dirty bit is set properly (if not, then we have
other bug that it won't even send down vulkan command to bind the
correct element buffer). We could further optimize the code path and
create a fast path for most common usages in the future.

Bug: chromium:1299261
Change-Id: Ifa8f86d431798c9ca4c128ed71a3e9e0a3537ccb
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3526021
Commit-Queue: Charlie Lao [email protected]
(cherry picked from commit 349636a05a3577a127adb6c79a1e947890bbe462)
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3605834
Reviewed-by: Achuith Bhandarkar [email protected]
Reviewed-by: Charlie Lao [email protected]

Notes: Backported fix for CVE-2022-1478.