MapCSS: add support for spatial expressions

[simon04]

A good support for a spatial "element of" expression could supersede the BuildingInBuilding test and allow mappers to write specific validators (see #9414, #9311).

[simon04]

In 6607/josm:

see #9516 - MapCSS: add basic support for a "contains" expression

The current syntax is outer ∋ inner, e.g., way[building?] ∋ node[building?].

This implementation is known to be inefficient since, for every match on the right side, it checks all primitives of the dataset for a match.

Nevertheless, this implementation allows mappers to write specific MapCSS-based tests involving this spatial operator.

[simon04]

In 6609/josm:

see #9516 - MapCSS: greatly improve performance of spatial "element of" (was: "contains") expression

The current syntax is inner ∈ outer.

The order plus symbol has been changed since now the left side is matched in the end.