Changing Color::IsDark() to match MS Word

[Luke Deller]

Hi,

I am a bit shy of proposing a changing to core LibreOffice code to fix
a doc/docx compatibility issue, so want to ask for opinions here.

fdo#61993 "doc/docx auto font color inverted in LibreOffice"

Do you think it is the right solution to change Color::IsDark()
in tools/source/generic/color.cxx to match what Microsoft Word does?

Neither the OpenDocument spec nor the Office Open XML spec define
what background colour should be considered "dark", leaving it up to the
implementation.

OpenDocument v1.2 section 20.385:
http://docs.oasis-open.org/office/v1.2/os/OpenDocument-v1.2-os-part1.html#__RefHeading__1420234_253892949

Regards,
Luke.