As agreed with Serg, renaming class Yesno to Yes_or_empty,
to reflect better its behavior.
This helper class is used to define INFORMATION_SCHEMA columns
that return either "Yes" or an empty string.
The 10.5 version of the patch.
Removing DEFAULT from INFORMATION_SCHEMA columns.
DEFAULT in read-only tables is rather meaningless.
Upgrade should go smoothly.
Also fixes:
MDEV-20254 Problems with EMPTY_STRING_IS_NULL and I_S tables