MdePkg/PeCoffLib: Capture DLL characteristics fields in image context

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=4405



When loading a PE/COFF image, capture the DLL characteristics fields of
the header into our image context structure so we can refer to them when
mapping the image.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Leif Lindholm <quic_llindhol@quicinc.com>
Reviewed-by: Oliver Smith-Denny <osde@linux.microsoft.com>
Reviewed-by: Michael Kubacki <michael.kubacki@microsoft.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>