Extend CopyImage tests to test astc_sliced_3d
Extend CopyImage tests to test astc_sliced_3d

These tests can be run for this extension, so they should be run.

Components: OpenGL
Affects: dEQP-GLES31.functional.copy_image.compressed.*astc*
         dEQP-GLES31.functional.copy_image.mixed.*astc*

Change-Id: Ibc9006678affe6bea27c6851ef7ed663cec0693e

KhronosGroup/VK-GL-CTS,KhronosGroup/VK-GL-CTS,KhronosGroup/VK-GL-CTS,KhronosGroup/Vulkan-CTS,KhronosGroup/Vulkan-CTS,KhronosGroup/Vulkan-CTS,KhronosGroup/Vulkan-CTS,KhronosGroup/VK-GL-CTS,KhronosGroup/Vulkan-CTS,KhronosGroup/VK-GL-CTS,KhronosGroup/VK-GL-CTS,KhronosGroup/Vulkan-CTS