PixelRoutine::stencilOperation() refactor
PixelRoutine::stencilOperation() refactor

stencilOperation() would sometimes perform unused stencilOperation()
calls. The logic was modified to make the stencilOperation() calls
only when we need them.

Bug: b/200826740
Change-Id: Ic9273dd8a0eec8819b9311ede49396ab07a4210f
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/66150
Tested-by: Alexis Hétu <1c7141772178a7e80858c3db5052b328076f08f4@google.com>
Reviewed-by: Nicolas Capens <51edc787c30f24c4904e8ffbb5523c3a9f7a451d@google.com>
Kokoro-Result: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Presubmit-Ready: Alexis Hétu <1c7141772178a7e80858c3db5052b328076f08f4@google.com>

google/swiftshader,google/swiftshader,google/swiftshader