Synchronize at end of renderpass
Synchronize at end of renderpass

Heavy-handed implementation of implicit or explicit VkSubpassDependency
to VK_SUBPASS_EXTERNAL after a subpass.

Fixes various test flake.

Test: dEQP-VK.glsl.derivate.*
Change-Id: I9cb60828e6aff344e28dd7a8e1a867b5c8a11c22
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/27708
Tested-by: Chris Forbes <c3279c50043e18e9442c1ae071cafa0e7a4ca967@google.com>
Presubmit-Ready: Chris Forbes <c3279c50043e18e9442c1ae071cafa0e7a4ca967@google.com>
Reviewed-by: Nicolas Capens <51edc787c30f24c4904e8ffbb5523c3a9f7a451d@google.com>
Kokoro-Presubmit: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

bkaradzic/SwiftShader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,google/swiftshader,google/swiftshader,bkaradzic/SwiftShader