This "bundles" all OSD properties. It also makes some previously
Lua-only values available (Lua has mp.get_osd_margins(), unsure if
anything uses it).
The main intention is actually to allow retrieving all fields in an
"atomic" way. (Could introduce a mechanism on the level of the mpv
client API to do this, but doing ti ad-hoc all the time like this commit
is easier.)
wm4
db9048f21a