ASAN caught reference outside scope issue regarding
RendererVk::initialize. Need to have a local copy of the string so that
it stays alive for the Vulkan call.

Bug: b/168145220
Change-Id: I13d751a48fe86a5a3d603d892c86c5a7186f2606
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2402353Reviewed-by: Ian Elliott <ianelliott@google.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>