[BUGFIX] Default size for group-type fields

Missing size property on group-type fields causes various
problems, like missing controls (move to top and move to
bottom) or misbehaving JS. Adding a default size ensures
that a forgotten size property does not break everything.

Additionally the size property is added to the sys_collection
table, since all Core tables should be cleanly defined.

Resolves: #23552
Documentation: #56627
Releases: 6.1, 6.2
Change-Id: Idafb1912f9702fddf85b7c2c222f408419e50ecf
Reviewed-on: https://review.typo3.org/28129
Reviewed-by: Markus Klein
Tested-by: Markus Klein