Adding functionality to stencils

Two minor features are required for the blitFramebuffer
implementation in OpenGL ES 3:
- lockStencil with x,y coordinates
- getting the stencil format (new getStencilFormat function)

Change-Id: I83ccccefe70dbbedd05b5d82bc75d30f689c4abe
Reviewed-on: https://swiftshader-review.googlesource.com/7490
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>

src/Renderer/Surface.hpp

diff --git a/src/Renderer/Surface.hpp b/src/Renderer/Surface.hpp
index cd89d74..dd96ffd 100644
--- a/src/Renderer/Surface.hpp
+++ b/src/Renderer/Surface.hpp
@@ -283,8 +283,9 @@
 		inline int getInternalSliceB() const;
 		inline int getInternalSliceP() const;
 
-		void *lockStencil(int front, Accessor client);
+		void *lockStencil(int x, int y, int front, Accessor client);
 		void unlockStencil();
+		inline Format getStencilFormat() const;
 		inline int getStencilPitchB() const;
 		inline int getStencilSliceB() const;
 
@@ -573,6 +574,11 @@
 		return internal.sliceP;
 	}
 
+	Format Surface::getStencilFormat() const
+	{
+		return stencil.format;
+	}
+
 	int Surface::getStencilPitchB() const
 	{
 		return stencil.pitchB;