This retires custom BUILD.gn files for the Vulkan Headers, Tools,
Validation-Layers, and Loader repos. They now have integrated BUILD.gn
files so switched ANGLE to use those by default.
Also Validation Layer, Loader, and Tools repos no longer uses codegen
so this speeds up the build overall.
Switched over from old VK_LAYER_LUNARG_standard_validation meta-layer
to VK_LAYER_KHRONOS_validation unified layer.

This changes includes a temporary workaround to the Vulkan-Loader repo
to remove its Window's build dependence on WDK. There are plans to
remove that depenedence in Loader master, but until then we can use
our custom branch workaround.
It also includes a custom branch for validation layers that includes
some build fixes for ANGLE.
Finally, the layers were crashing on Android when attempting to use
DebugUtils extension so forcing DebugReport on Android for now.

Bug: angleproject:2449
Bug: angleproject:3320
Bug: angleproject:3852
Change-Id: I48b36acefcc7f2bc930eb72d6fdbc87bca24f833
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1610438Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Tobin Ehlis <tobine@google.com>