The ETC2 decoder already existed in SwiftShader, so this cl hooks it
up in vk::Image. In order to be transparent to the user, any time a
compressed image is created, another image is simultaneously created,
which will eventually contain the decompressed image.

Bug b/119620767

Tests: dEQP-VK.pipeline.sampler.view_type.2d.format.etc2_r8g8b8a1_unorm_block.*
Tests: dEQP-VK.pipeline.sampler.view_type.2d.format.etc2_r8g8b8a8_unorm_block.*
Tests: dEQP-VK.pipeline.sampler.view_type.2d.format.eac_r11g11_unorm_block.*

Change-Id: I8bfdccccd9cad30e5b707ba82aac2b581ec2a90e
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/29428
Presubmit-Ready: Alexis Hétu <sugoi@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>