This change adds loext:margin-left and loext:margin-right, which
implement margins that support font-relative units.
See tdf#36709 for additional details.
Change-Id: I31b0dd2b6f98cb5b02fd4dca3608db6fdee4054c
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/177473
Tested-by: Jenkins
Reviewed-by: Jonathan Clark <jonathan@libreoffice.org>