Main issue:
- Trimming spaces from end of text fields was done not only for CHAR
fields but also for other types.

Other issues:
- Compare function was not working correctly for indexes using prefix of
the field.
- Index class was calling indexed column destructors twice.
- Table and other classes were using pointers to TABLE and its elements
instead of TABLE_SHARE which has longer life-cycle.

Changes:
- Fixed the handling of no pad collations.
- Fixed compare for prefix keys.
- Fixed Index destructor.
- Switched Table to use TABLE_SHARE instead of TABLE.
- Test added.

RB#18759