Bit count for the image is a numeric value (sal_uInt16) but only a handful of values make sense - namely 1,4,8,24 and 32. This replaces the numeric value with an enum, which only accepts those values and checks the correct values are used at compile time. Change-Id: I0fc137c62bce3b0d021f05019a1648da628521bc Reviewed-on: https://gerrit.libreoffice.org/c/core/+/112408 Tested-by: Jenkins Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>