Implement various vulkan stencil clears and fix various stenciling bugs.

src/gpu/vk/GrVkCommandBuffer.h

Index: src/gpu/vk/GrVkCommandBuffer.h
diff --git a/src/gpu/vk/GrVkCommandBuffer.h b/src/gpu/vk/GrVkCommandBuffer.h
index 33867abc5acc23c09af4087c17393ed5f26d8974..476bb7a50c9d8888b06960cff1a1bf5e68b8968d 100644
--- a/src/gpu/vk/GrVkCommandBuffer.h
+++ b/src/gpu/vk/GrVkCommandBuffer.h
@@ -114,6 +114,12 @@ public:
                          uint32_t subRangeCount,
                          const VkImageSubresourceRange* subRanges);
 
+    void clearStencilImage(const GrVkGpu* gpu,
+                           GrVkImage* image,
+                           const VkClearDepthStencilValue* color,
+                           uint32_t subRangeCount,
+                           const VkImageSubresourceRange* subRanges);
+
     void copyImage(const GrVkGpu* gpu,
                    GrVkImage* srcImage,
                    VkImageLayout srcLayout,