row_upd_rec_in_place(), page_zip_write_rec(): Add parameter "index".

page_dir_set_n_heap(): Add a debug assertion that on compressed
pages, n_heap will always be incremented by one.  Improve code formatting.

page_zip_dir_add_slot(): New function, called from
page_cur_insert_rec_low() after page_mem_alloc_heap().

rec_set_n_owned_new(): Do not call page_zip_rec_set_owned()
on the supremum record.

rec_offs_make_valid(): Add debug assertions.

page_zip_dir_user_size(): Correct an off-by-one error in the debug assertion.

page_zip_apply_log(): Add parameter trx_id_col.  Skip trx_id and roll_ptr.

page_zip_decompress(): Simplify the handling of "storage" in the loop that
copies the uncompressed fields.

page_zip_write_rec(): Store trx_id and roll_ptr separately.

page_zip_write_trx_id(), page_zip_write_roll_ptr(): Fix off-by-one errors.

page_cur_insert_rec_low(): Call page_zip_dir_add_slot() after
page_mem_alloc_heap().  Remove some redundant assertions.
Pass page_zip to page_dir_split_slot().