IfcRepresentationMap : MappingOrigin is unclear

An old issue been part since forever but

Description in documentation to anyone not native in english is a bit unclear.
"defines the position about which the mapped representation is mapped."

Either
a. Placement describes a transformation to place geometry to its placement and is used as is.
b. Placement is the geometry's placement and is combined with mapping target using inverse placement.
Last time we tested this both versions were used by importers.

1. A better description would be nice. Currently there is no sample included in documentation that uses mapping source which would define the correct use. Change one of the columns in [file](https://standards.buildingsmart.org/IFC/RELEASE/IFC4_3/HTML/annex_e/mapped-geometric-shape/mapped-shape-with-multiple-items.html)
2. Make this optional. This placement is effective irrelevant as the mapping target tarformation is always used (unless this class is used in something else). Now everyone writes unnecessary default placement always.
3. Deprecate this if there is no actual use