area/length filters should be based on unclipped geometries

[tyrasd]

The goal of these filters is to select OSM features with the specified properties (e.g. buildings having a footprint larger than a given size). Currently, area: and length: filters are performed on geometries which are clipped to the query's area of interest, which partly negates the functionality of these filters. Instead, the filters should take the full, unclipped, geometry of OSM features into account.

I'm marking this as a bug because the current behaviour clearly doesn't match the documentation:

matches all features with [an area / a length]

PS: This could in some edge cases also affect the geometry-type filter (geometry:), where because of clipping a geometry could potentially degenerate to a different type (for example, a polygon could collapse into a line or point when the polygon and the area of interest are only touching along their border or a single vertex).

See also ohsome-api#245.