coin: Add x86_64 config for HarmonyOS

Add an x86_64 HarmonyOS target build to the CI configurations. The
x86_64 emulator target is useful for on-host testing without physical
devices.

For this to link, the target needs x86_64 counterparts of the vcpkg
OHOS ports. So far the provisioning installed the arm64-ohos-qt triplet
only, and the x86_64 build linked its objects against the arm64 ICU
archives, failing with "is incompatible with elf_x86_64".

Install the x64-ohos-qt triplet next to arm64-ohos-qt and expose its
installed directory as VCPKG_OHOS_INSTALLED_X64. Copy the OpenSSL
headers into both installed directories, and point the x86_64 config's
CMAKE_FIND_ROOT_PATH at the x64 directory.

Task-number: QTBUG-150347
Change-Id: I66d9aa51507e7c9157265722067a06a94e07896b
Reviewed-by: Simo Fält <simo.falt@qt.io>
Reviewed-by: Liang Qi <liang.qi@qt.io>