We try and copy the shared one to the user location the first time we create a
customized user file. If the dir doesn't exist then that migration doesn't
happen. The new autocorr file is then written, creating the dir, and any
further operations will reattempt the skipped share copy, and this time succeed
because the dir now exists.  Which overwrites the previously written customized
content.

This is similar to fdo#65501 "ensure configured backup dir exists before using
it", so reuse that code and move it into unotools.

Change-Id: I38fa621b8d7295d70b09172a028569ea95404120