btr_cur_upd_rec_in_place(): Avoid calling page_zip_write_rec() if we
are not modifying any fields that are stored in compressed format.

btr_cur_update_in_place_zip_check(): New function to check if a
ROW_FORMAT=COMPRESSED record can actually be updated in place.

btr_cur_pessimistic_update(): If the BTR_KEEP_POS_FLAG is not set
(we are in a ROLLBACK and cannot write any BLOBs), ignore the potential
overflow and let page_zip_reorganize() or page_zip_compress() handle it.
This avoids a failure when an attempted UPDATE of an NULL column to 0 is
rolled back. During the ROLLBACK, we would try to move a non-updated
long column to off-page storage in order to avoid a compression failure
of the ROW_FORMAT=COMPRESSED page.

page_zip_write_trx_id_and_roll_ptr(): Remove an assertion that would fail
in row_upd_rec_in_place() because the uncompressed page would already
have been modified there.

This is a 10.5 version of commit ff3d4395
(different because of commit 08ba3887).