[LyX/master] Add default TransformID enum value

[Pavel Sanda]

On Thu, Nov 26, 2020 at 08:45:44PM +0200, Yuriy Skalko wrote:
> >>Seems like std::regex was already always used for most recent compilers, so
> >>how about getting rid of boost::regex
> >
> >Looks reasonable from GCC point of view. Can's speak about MSVC (IIRC no one
> >replied about MSVC 2017, right?)
> 
> Right. But at least with CMake only std::regex is already used (from summer
> 2019) for MSVC compilers.

Given that it's just us who is preparing win binaries, then MSVC version is
probably not that important, except if by chance Yu was using it.

> I'm not an expert in build systems, so my patch doing this will require some
> correction.

Autotools looks fine on a first sight, JMarc might have some comment.
Pavel