Resolve must occur in linear space.

Bug b/119620965

Change-Id: I5c7c7c45a1448f44c702969e34e580dc299df70a
Test: dEQP-VK.renderpass.suballocation.multisample_resolve.*
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/31871Tested-by: Alexis Hétu <sugoi@google.com>
Presubmit-Ready: Alexis Hétu <sugoi@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Chris Forbes <chrisforbes@google.com>