tdf#160593: make sure to use current element's font size for em unit
According to https://drafts.csswg.org/css-values-4/#font-relative-length
em is "equal to the computed value of the font-size property of the element
on which it is used". This means, that for an element that defines its own
font-size, attributes like 'dy' using em refer to the new font-size, not to
inherited font-size.
Change-Id: Ie5a013df99a68edddf466e4c0ee5311f6219fcb2
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/166233
Tested-by: Jenkins
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>