* Associate DXGI function parameters and struct fields with the corresponding enum type
These are more convenient and descriptive to use than plain `UINT`s.
* dxgi: Annotate `*_FLAG` enums with missing `[Flags]` attribute
* dxgi: Scrape some loose flag constants into enums
* dxgi: Annotate GetDesc::pDesc with RetVal attribute
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Co-authored-by: Mike Battista <13860912+mikebattista@users.noreply.github.com>