libstdc++: move FramebufferHelper to cache utils vk_helper.h includes vk_cache_utils.h. FramebufferHelper was declared in vk_helper.h. And FramebufferCache, in vk_cache_utils.h, requires FramebufferHelper for its payload hashmap. This was solved with a forward declaration. But, with std::pair definition in libstdc++ this is not enough. Bug: chromium:957519 Change-Id: I32e3e247c3c8bef8b52806aa2601e4012e6aa79e Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3727671 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>