Enumeration Image_PixMap::ImgFormat, previously declared as nested
enumeration within class *Image_PixMap*,
has been moved to global namespace as Image_Format following OCCT coding rules.
The enumeration values have suffix Image_Format_ and preserve
previous name scheme for easy renaming of old values.
E.g. Image_PixMap::ImgGray become Image_Format_Gray.
Old definitions are preserved as depreacated aliases to the new ones.
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