GCC fails to automatically map the initializer assignment for
initializing the angle::PackedEnumMap. So this change adds the
type hint ImageMemoryBarrierData to the second part of the pairs
passed to construct the PackedEnumMap.

GCC error:
    ./../third_party/angle/src/libANGLE/renderer/vulkan/vk_helpers.cpp:387:1: error: could not convert ‘{{rx::vk::ImageLayout::Undefined, {"Undefined", ...}}}’ from ‘<brace-enclosed initializer list>’
    to ‘const angle::PackedEnumMap<rx::vk::ImageLayout, rx::vk::{anonymous}::ImageMemoryBarrierData>’
      387 | };
          | ^
          | |
          | <brace-enclosed initializer list>

Bug: chromium:819294
Change-Id: I314c43c0795e54cabd891205ee935c6354d11658
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2401778Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>