Add imagery boundary selector during editing

[wiktorn]

Add a imagery boundary editor:

• map with visualization of the boundary
• use nominatim to search for relations which would became the boundary
• simplify geometry (allow changing max-error)
• export as maps entry to be copied into our wiki
• provide size of created geometry

See: #16324, #16249,

[Don-vip]

Should the boundary editor also offer an imagery preview? See #9972

[Don-vip]

Also see my plugin ​osmwiki:JOSM/Plugins/Imagery-XML-Bounds which could be deprecated in favor of this new core feature. Maybe you can reuse some code :)

[Klumbumbus]

Replying to wiktorn:

• use nominatim to search for relations which would became the boundary

Just to keep in mind that only in rare cases the boundaries of the imageries match admin boundaries. Mostly the imagery boundary is larger either with a constant "simplified" distance to the admin boundary or staircase shaped (https://josm.openstreetmap.de/mapsview?entry=Saxony%20historical%20aerial%20imagery%202005) or not related at all.
Compare also e.g. the three Erlangen entries at wiki:Maps/Germany.