[vulkan] use VMA at third-party (#83934)
Remove the VMA checked in at `aten/src/ATen/native/vulkan/api/vk_mem_alloc.h`, and use the version checked into `fbsource/third_party` instead.
Also change open source CMakeLists to look for VMA in third_party submodule directory.
Note that I had to add an alternate VulkanMemoryAllocator target that uses `fb_xplat_cxx_library` instead of `oxx_static_library` to make it work with vulkan targets in `caffe2`.
Before landing this diff, make sure https://github.com/pytorch/pytorch/pull/83906 is committed on open source, which adds VMA as a git submodule of pytorch.
Differential Revision: [D38943217](https://our.internmc.facebook.com/intern/diff/D38943217/)
**NOTE FOR REVIEWERS**: This PR has internal Facebook specific changes or comments, please review them on [Phabricator](https://our.internmc.facebook.com/intern/diff/D38943217/)!
Pull Request resolved: https://github.com/pytorch/pytorch/pull/83934
Approved by: https://github.com/manuelcandales
