Be consistent on Tag and Geometry retrieval for OSMContribution

[SlowMo24]

Problem Description

To extract OSHDBTags from an OSMContribution one needs to extract the OSMEntity first like contribution.getEntityBefore().getTags().

The extraction of the Geometry from an OSMContribution is located directly with the OSMContribution e.g. contribution.getGeometryUnclippedBefore().

This seems incoherent and makes client code less readable.

Expected Solution

Move Geometry-retrieving methods from OSMContribution to OSMEntity.

Alternative Solutions

Move OSHDBTags retrieving methods to OSMContribution.