Add macros from wingdi.h (e.g. RGB, GetRValue)

I would appreciate it if you could add the following macros defined in wingdi.h to CsWin32.

#define RGB(r,g,b)          ((COLORREF)(((BYTE)(r)|((WORD)((BYTE)(g))<<8))|(((DWORD)(BYTE)(b))<<16)))
#define PALETTERGB(r,g,b)   (0x02000000 | RGB(r,g,b))
#define PALETTEINDEX(i)     ((COLORREF)(0x01000000 | (DWORD)(WORD)(i)))
#define GetRValue(rgb)      (LOBYTE(rgb))
#define GetGValue(rgb)      (LOBYTE(((WORD)(rgb)) >> 8))
#define GetBValue(rgb)      (LOBYTE((rgb)>>16))
#define GDI_WIDTHBYTES(bits) ((DWORD)(((bits)+31) & (~31)) / 8)
#define GDI_DIBWIDTHBYTES(bi) (DWORD)GDI_WIDTHBYTES((DWORD)(bi).biWidth * (DWORD)(bi).biBitCount)
#define GDI__DIBSIZE(bi) (GDI_DIBWIDTHBYTES(bi) * (DWORD)(bi).biHeight)
#define GDI_DIBSIZE(bi) ((bi).biHeight < 0 ? (-1)*(GDI__DIBSIZE(bi)) : GDI__DIBSIZE(bi))
#define GetKValue(cmyk)      ((BYTE)(cmyk))
#define GetYValue(cmyk)      ((BYTE)((cmyk)>> 8))
#define GetMValue(cmyk)      ((BYTE)((cmyk)>>16))
#define GetCValue(cmyk)      ((BYTE)((cmyk)>>24))
#define CMYK(c,m,y,k)       ((COLORREF)((((BYTE)(k)|((WORD)((BYTE)(y))<<8))|(((DWORD)(BYTE)(m))<<16))|(((DWORD)(BYTE)(c))<<24)))

Start by locating how CsWin32 represents or generates existing Win32 constants and helper APIs, then check any related tests. Implement support for the macros listed in the issue, including RGB, palette, color-component, DIB-size, and CMYK helpers; done means the requested macros are available to generated C# consumers and covered by tests.