Multilinestring Support

[MikeTho16]

Describe the bug
OSM has a limit of 2,000 nodes per way. Many linear features with which our project deals have more than 2,000 vertices and when such features are exported they should not be split. One method of addressing this limitation is to introduce a new relation type=multilinestring which would be similar to type=multipolygon.

To Reproduce

1. Import/upload linear feature with more than 2,000 vertices
2. Export above data (e.g. to a shapefile)

Expected behavior
Import

• linestrings/polylines are broken into ways of 2,000 nodes or less.
• A relation is created with type=multilinestring
• Above ways are added to above relation
• Tags from the original feature are added to the relation
• Ways receive no tags

Export

• Relations with type=multilinestring become a single linestring/multilinestring/polyline in the output
• Tags (other than type=multilinestring) from the relation are turned into the corresponding field values on the above linestring

Translations via API

• Relation type=multilinestring should be treated as a linear feature

Screenshots
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Additional context
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