For some simple benchmarks, a majority of time was
spend in find_head() which tries to find the best
place to put the record.

The result of this patch is a 2x or more speedup for
inserts without keys for format PAGE. All changes
are only related to how rows are stored

Should fix some of the problems mentioned in:
MDEV-8132 Temporary tables using Aria with very poor performance
MDEV-9079 Aria very slow for internal temporary tables
MDEV-5841 Mariadb very poor temporary performance

The following changes where done:
- For rows with a small row length that fits into
  a page (818 bytes with 8192 pages), stop as soon as we
  hit a match.
- Added markers full_head_size and full_tail_size that tells
  us where to start searching on the bitmap page
- Ensure that page->used_size is correctly updated when
  bitmap grows. This allows us to stop searching at used_size
- Added code to check that the bitmap variables are correct.
- Fixed a wrong test where we set "first_bitmap_with_space".
  This shouldn't have caused any notable problems.