Add vulkan_headers_ndk cc_library_headers module

We had a cc_library_headers module for the Vulkan headers, for use by
platform and vendor modules. We also had an ndk_headers module to copy
the headers into the NDK. This adds another cc_library_headers module
which allows things in the Android tree but which are built against
the NDK (like CTS) to use our copy of the header, rather than an NDK
prebuilt. That allows CTS tests to use extensions that aren't yet
present in the prebuilt NDK Vulkan header.

Bug: 34745152
Test: build with accompanying external/vulkan-validation-layers changes
Change-Id: Ia5f1bc086210403f8e6c023ce3c6413f74f91ff3