The blitter now has the ability to compute borders and corners
for seamless cubemaps.

Bug b/119620767

Tests: dEQP-VK.pipeline.sampler.view_type.cube.format.*

Change-Id: Idf47886526cf7fd9bce6739a558716189f02a64c
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/30349
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>