Changes to the name of the `navmesh` and `navpoly` properties on
`NavigationRegion` caused navigation data to be lost on load.
This PR creates uses `_set`/`_get` to handle compatibility with the
older names on load, preserving the data.
Also fixes a typo on `get_vertices_per_polygon` in `NavigationMesh`,
and renames the property to remove the `polygon_` prefix which doesn't
match the setter/getter.
- DarkKilauea, akien-mga
0572346985
Schema for navigation to name user facing API with "navigation" without abbreviation and e.g. NavigationServer internals with abbr "nav".
- smix8
34e7628f5f
