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>

MdePkg/Include/Library/PeCoffLib.h

@@ -171,6 +171,12 @@ typedef struct {
   ///
   UINT16                      ImageType;
   ///
+  /// Set by PeCoffLoaderGetImageInfo() to the DLL flags stored in the PE/COFF header and
+  /// in the DllCharacteristicsEx debug table.
+  ///
+  UINT16                      DllCharacteristics;
+  UINT32                      DllCharacteristicsEx;
+  ///
   /// Set by PeCoffLoaderGetImageInfo() to TRUE if the PE/COFF image does not contain
   /// relocation information.
   ///