This is a combination of 3 commits.

Move implementation to CheckLinkFormulaNeedingCheck() for further reuse

(cherry picked from commit 55e484c7)

CheckLinkFormulaNeedingCheck() for .xlsx cell formulas

(cherry picked from commit f96dbc3d)

CheckLinkFormulaNeedingCheck() for .xls cell formulas

(cherry picked from commit 6bc48275)

a6dd195f7eb4d43483e87eeca59f651e7bf2dcb8
2587fbc4fec39b6f2c8e733331815a2953dee308

Change-Id: I541d2b6e12a88371c064b901b00e71206ee0c18e
Reviewed-on: https://gerrit.libreoffice.org/48143Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>