EmiteImageWrite() was writing to inactive lanes, which was causing
several tests to fail. state->activeStoresAndAtomicsMask() returns
the proper lane mask.

Bug: b/184063472
Tests: dEQP-VK.glsl.builtin_var.fragdepth.*

Change-Id: I24882cb963ed30052c4774318e1267041c89ee02
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/54368Tested-by: Sean Risser <srisser@google.com>
Commit-Queue: Sean Risser <srisser@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>