Also
- convert to o3tl::cow_wrapper
- drop the second param to the constructor and just
  let vector use it's own resize logic
- bump MAX_POLYGONS from 0x3FF0 to 0xffff so that the
  ios2met filter can load it's files properly.

Change-Id: I9db19e4f7b4f946e801ea07c31d2d0ded7837a0e
Reviewed-on: https://gerrit.libreoffice.org/47789Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
Tested-by: Noel Grandin <noel.grandin@collabora.co.uk>