WebGPU GL: Add RenderAttachment texture usage.

Add RenderAttachment internal texture usage to DawnGLTextureRepresentation.

This allows transfers to offscreen imageBitmap with alphaMode="opaque"
to work correctly.

Bug: dawn:2187
Change-Id: Ice4d5db55bae9c8e49bd8f176d041532a2f86968
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5020359
Commit-Queue: Stephen White <senorblanco@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1223156}

gpu/command_buffer/service/shared_image/dawn_gl_texture_representation.cc

@@ -51,7 +51,8 @@ wgpu::Texture DawnGLTextureRepresentation::BeginAccess(
 
   // Add internal TextureBinding usage for copyTextureForBrowser().
   wgpu::DawnTextureInternalUsageDescriptor internalDesc;
-  internalDesc.internalUsage = wgpu::TextureUsage::TextureBinding;
+  internalDesc.internalUsage =
+      wgpu::TextureUsage::TextureBinding | wgpu::TextureUsage::RenderAttachment;
 
   texture_descriptor.nextInChain = &internalDesc;