vulkan: Support VK_EXT_debug_report in loader and nulldrv

* Add extension to vulkan.api.
* Fix a few errors in upstream vk_ext_debug_report.h; bugs filed.
* Loader enumerates extension iff the driver supports it.
  - TODO: Also enumerate if any layers that support it are implicitly
    enabled.
  - Note extension may still be enabled if any layer supports it.
* Add loader bottom procs for the extension functions. These will call
  through to the driver version if the driver supports the extension.
* Add no-op support to nulldrv, mostly for testing the loader.

Change-Id: I092d2da56ee4c64498f8edae75e0d995478bb6f2
(cherry picked from commit a5ef7c27bc85e3628814532a32ffb9a5c33c4b73)