Rootless GPU Debug

Add the ability to load GPU debug layers from the base
directory of debuggable applications.

This update concides with changes to framework/base to
control the enabling logic in GraphicsEnvironment.

This commit changes the Vulkan loader to:
* Scan an additional location for debug layers.
* Use the provided order of layers from GraphicsEnvironment,
  overriding system properties.
* Use the first instance of a layer found, in the case of duplicates.
* Move layers paths and namespace to GraphicsEnv, removing vulkan_loader_data

Bug: 63708377
Test: Manual, CTS tests to follow

Change-Id: I38dc91bbc26671f5093ee1b12454fc024c0b5892