To be able to look which fonts are in use, we need to collect the
autostyles which contains all styles that are used in a document.
Previously the autostyles were collected in the same process as
they were expoted, so with this commit we separate collaction and
export. First we collacte the auto styles, then e can use them in
embedded fonts export, the last we export the auto styles
themselves.

Change-Id: Ib939f1119f4af00a1e5d66fcd2e04b9d2add6881
Reviewed-on: https://gerrit.libreoffice.org/57348
Tested-by: Jenkins
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>