Bug 18336: Shift *TEXT columns size

Bug 18336: Shift *TEXT columns size

Because of the 3-byte vs. 4-byte char size change in utf8mb4, altering a
column's encoding from utf8 into utf8mb4 results in this changes:

TEXT => MEDIUMTEXT
MEDIUMTEXT => LONGTEXT

The column size in the rows (the text itself goes to a separate object
storage) shifts by 1 byte, because all chars are shifted in bytes size
too, so there needs to be room for the byte-count in the column.

This is a debatable change, but the path needs to be included along with
the rest of the patchset for consistency.

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>