Add GrVkCopyPipeline to handle vulkan copies as draws

src/gpu/vk/GrVkUtil.cpp

Index: src/gpu/vk/GrVkUtil.cpp
diff --git a/src/gpu/vk/GrVkUtil.cpp b/src/gpu/vk/GrVkUtil.cpp
index 0d07e1f57a7318d4b3b613af361143fdb89be313..a14f827dcb02dd7507ed081a003c7e2ba8db77af 100644
--- a/src/gpu/vk/GrVkUtil.cpp
+++ b/src/gpu/vk/GrVkUtil.cpp
@@ -312,7 +312,7 @@ bool GrCompileVkShaderModule(const GrVkGpu* gpu,
 
         shaderc_shader_kind shadercStage = vk_shader_stage_to_shaderc_kind(stage);
         result = shaderc_compile_into_spv(compiler,
-                                          shaderString.c_str(),
+                                          shaderString,
                                           strlen(shaderString),
                                           shadercStage,
                                           "shader",