Remove TextureViewBuilder and add CreateDefaultTextureView entry point

This patch is the first one to descriptorze texture view. In this
patch, we completely remove TextureViewBuilder and add the entry
point CreateDefaultTextureView for creating a texture view on a
non-array 2D texture using the same type and format.

Texture view descriptors and 2D array texture views will be supported
in the next patch.

BUG=dawn:1, dawn:16

Change-Id: Ibd2a0bcf02cbb567a98d2faaaaa897eff2c062e5
Reviewed-on: https://dawn-review.googlesource.com/1440
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Commit-Queue: Jiawei Shao <jiawei.shao@intel.com>

examples/glTFViewer/glTFViewer.cpp

@@ -438,7 +438,7 @@ namespace {
                 .GetResult();
             queue.Submit(1, &cmdbuf);
 
-            textures[iTextureID] = oTexture.CreateTextureViewBuilder().GetResult();
+            textures[iTextureID] = oTexture.CreateDefaultTextureView();
         }
     }