Reland "Rename GrStencilAttachment class to generic GrAttachment"

This is a reland of 6113d50ec48be049c13a6e4bbea191df93e68674

Original change's description:
> Rename GrStencilAttachment class to generic GrAttachment
>
> Additional this adds a UsageFlags member to the new GrAttachment
> class.
>
> Bug: skia:10727
> Change-Id: Ifc0bfffd959f5fbc46bfcdf269e1b2a933929753
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/323107
> Commit-Queue: Greg Daniel <egdaniel@google.com>
> Reviewed-by: Brian Salomon <bsalomon@google.com>

Bug: skia:10727
Change-Id: Ie0ff0885e01c9f0666fb0cfaa765e463dcc6d0a5
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/324277
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
diff --git a/src/gpu/GrRenderTask.cpp b/src/gpu/GrRenderTask.cpp
index 4397cf9..d63aa2e 100644
--- a/src/gpu/GrRenderTask.cpp
+++ b/src/gpu/GrRenderTask.cpp
@@ -7,8 +7,8 @@
 
 #include "src/gpu/GrRenderTask.h"
 
+#include "src/gpu/GrAttachment.h"
 #include "src/gpu/GrRenderTarget.h"
-#include "src/gpu/GrStencilAttachment.h"
 #include "src/gpu/GrTextureProxyPriv.h"
 #include "src/gpu/GrTextureResolveRenderTask.h"