fdo#76101 [DOCX] Export: Limit no of styles in styles.xml

MS Office has an internal limitation of 4091 styles in styles.xml
and cannot load a .docx with more. However the documentation seems to allow
that. So if there are more styles, don't export those.

MS Office follows the same principle and repairs the corrupt document by
removing extra styles.

Change-Id: I20c8775ee9d697a6613be96eb01283844c1d78f5
Reviewed-on: https://gerrit.libreoffice.org/8653
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>