In HLSL output, structs in interface blocks are not accessed directly.
Rather they get copied from the D3D constant buffer to static structs
in the shader header. Fix generating the copy/init code in the header
to handle arrays of structs correctly.

BUG=angleproject:2084
TEST=angle_end2end_tests

Change-Id: If66bd5be3f3570ba591b8b62c5284c06fc83dd45
Reviewed-on: https://chromium-review.googlesource.com/608448Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>