MdeModulePkg/DxeCore: invoke the emulator protocol for foreign images

When encountering PE/COFF images that cannot be supported natively,
attempt to locate an instance of the PE/COFF image emulator protocol,
and if it supports the image, proceed with loading it and register it
with the emulator.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Hao Wu <hao.a.wu@intel.com>