Only enabled for specific tests at the moment. This CL allows our tests
to sanitizes memory for the robust resource access extension. It is
quite slow so should not be enabled by default.

Only works for 1 level 2D color textures and buffers. Makes several
flaky robust resource initialization tests consistently fail.

Controlled via an angle::Feature in FeaturesVk.

It works by initializing memory to an abitrary non-zero value:

 - if newly allocated memory is mappable, we map it in init and set it
 - if a buffer or texture can be a transfer destination, we use a
   staging resource
 - otherwise we don't attempt to initialize the resource.

Bug: angleproject:4384
Change-Id: I9b4f347bfcddf3096f491ed0243bef86837feaa0
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2043271
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Cody Northrop <cnorthrop@google.com>