Implement buffer lazy initialization before CopyBufferToTexture()

This patch adds the check and implementations of buffer lazy
initialization before CopyBufferToTexture().

The support of buffer lazy initialization before CopyTextureToBuffer()
is much more complicated than what we do for CopyBufferToTexture(), so
we decide to put it in another CL instead of writing them together with
CopyBufferToTexture().

BUG=dawn:414
TEST=dawn_end2end_tests

Change-Id: I45fdcdde2c9a0dafff23623815fc35c877990ef1
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/25140
Commit-Queue: Jiawei Shao <jiawei.shao@intel.com>
Reviewed-by: Austin Eng <enga@chromium.org>

src/dawn_native/opengl/CommandBufferGL.cpp

@@ -518,6 +518,8 @@ namespace dawn_native { namespace opengl {
                     GLenum target = texture->GetGLTarget();
                     const GLFormat& format = texture->GetGLFormat();
 
+                    buffer->EnsureDataInitialized();
+
                     ASSERT(texture->GetDimension() == wgpu::TextureDimension::e2D);
                     SubresourceRange subresources = {dst.mipLevel, 1, dst.origin.z,
                                                      copy->copySize.depth};