All Web IDL constants are missing

I was using confluence to research https://github.com/w3c/svgwg/issues/291 a bit today, to see if https://svgwg.org/svg2-draft/types.html#InterfaceSVGUnitTypes was implemented everywhere.

The interface object is there (everywhere), but the constants aren't listed. They are own properties of the interface object, and I do see SVG_UNIT_TYPE_UNKNOWN in the data collected in https://github.com/mdittmer/web-apis.

Other interfaces I checked to confirm missing constants: Event, Node. HTMLMediaElement.

Per https://github.com/GoogleChromeLabs/confluence/issues/202#issuecomment-332992863 this seems to not be an accident, but it still seems like something to fix.

The issue identifies SVGUnitTypes, Event, Node, and HTMLMediaElement as affected interfaces; start by tracing the Web IDL interface collection entry point and compare interface own properties with the collected data. Done means constants such as SVG_UNIT_TYPE_UNKNOWN are reported for these interfaces, with coverage for the missing Web IDL constants.

Written by the indexing model from the issue text.