Support linestring in merge analyser

[frodrigo]

Merge analyser only work with nodes. Add support of linestrings.

[frodrigo]

@didier2020 convert linestring to point on import then conflate only with point is easy. Other part require more works.

[didier2020]

i agree but if the source to merge is linestring, conflation is on one or more way ?
(a point is not enough to identify the beginning and the end)

[frodrigo]

We have to review all the https://github.com/osm-fr/osmose-backend/blob/master/analysers/Analyser_Merge.py
But it is one of the most complex part of the Backend.

Main changes:

• Import line (or poly)
• conflate geometry, choose a way to compare

[didier2020]

ok, so i just fix linestring for geojson.