The immutable textures are intended to be "immutable". Right now we are
still re-allocating VkImage object based on base_level and max_level.
This causes a problem for rendering to a level that is beyond
[base_level, max_level], which is totally within OpenGL spec. This CL
makes an immutable texture always allocate from 0 to max levels that are
specified by a glTexStorage call. Changing base_level will not trigger
re-allocation of VkImage object.

Bug: b/181800403
Change-Id: I4b4ddea17b7f6f7bfd8f36bfe8bb3a35b5c180b6
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2368038Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Ian Elliott <ianelliott@google.com>
Commit-Queue: Charlie Lao <cclao@google.com>