Add missing NEWSEQUENTIALID function in MSSQLServer mode.

[mwisnicki]

Does not attempt to be sequential but that should be good enough.

[katzyn]

Thank you for your contribution!

Please send a licence statement as described here
https://h2database.com/html/build.html#providing_patches
to our mailing list / Google group:
https://groups.google.com/g/h2-database

[mwisnicki]

Thank you for your contribution!

Please send a licence statement as described here https://h2database.com/html/build.html#providing_patches to our mailing list / Google group: https://groups.google.com/g/h2-database

Done.

I was actually looking for contributor guide before submitting but didn't find it.

Please consider adding standard CONTRIBUTING file with link or copy of instructions.