XArch: support UiApp replacement across firmware builds

[MarsDoge]

Summary

• Extend MODERN_SETUP_REPLACE_UIAPP=1 support beyond LoongArchVirt to OVMF X64, ArmVirt AARCH64, and RiscVVirt RISCV64.
• Preserve the product architecture validated in Phase30: ModernSetupApp provides the UiApp/Firmware Setup frontend while native BootManagerMenuApp remains responsible for Boot#### launch.
• Add smoke coverage for the generated replacement overlays.

Release impact

This follow-up is needed before tagging a binary release where all firmware assets are UiApp-replacement builds:

• OVMF X64: OVMF_CODE.fd
• ArmVirt AARCH64: QEMU_EFI.fd
• LoongArchVirt LOONGARCH64: QEMU_EFI.fd
• RiscVVirt RISCV64: RISCV_VIRT_CODE.fd

Validation

• python3 Tests/Smoke/smoke_validate.py
• git diff --check