Add priority=forward / priority=backward in presets

[richlv]

Please add priority=forward and priority=backward to allow auto-completing those values in the tag dialog.

The tag seems to be non-controversial, is documented at ​https://wiki.openstreetmap.org/wiki/Key:priority and fairly widely used:

Tag priority=forward appears 2226 times in the planet. ​https://taginfo.osm.org/tags/priority=forward
Tag priority=backward appears 1874 times in the planet. ​https://taginfo.osm.org/tags/priority=backward

[skyper]

Once again, a tag with *=forward/backward on nodes. Can it not only be place on ways, even if they are short?

[richlv]

Oh, I didn't even notice it being suggested for usage on nodes. That might be problematic, as somebody could add it on way end node, requiring extra validity checks...
I've only applied it on ways, and wouldn't mind the preset only suggesting it on ways - that way slightly nudging towards the desired use :)