Vulkan: Simplify TextureVk::initImage() call. This CL moves the logic that check if immutable texture or not and decide what levels should be allocated from callers in various places to TextureVk::initImage() to simplify the code a bit. Bug: b/196456356 Change-Id: Ida31a5a06402cc627d0493032f8424baae3e7264 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3141974 Commit-Queue: Charlie Lao <cclao@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Tim Van Patten <timvp@google.com>