[visual-qa] EditVertex right-click insert misses CIRCULARSTRING because locater hits chords not arcs

[grootstebozewolf]

Part of #68. Follow-on to #82 (odd-count insert).

Observed

Move/add/delete vertex, right-click add on a CIRCULARSTRING (or GEOMETRYCOLLECTION of one) clicks the drawn arc and nothing is inserted. The same click on the control chord (as in #82) inserts.

Cause: GeometryPointLocater.checkSegment uses LineSegment (control chords). The painted geometry is the circular arc, which can sit far from the chord. First-contact: right-click does not add.

Expected

locateNonVertexPoint hits the circular arc (3-control window), not the chord. Insert still splits that arc (net +2, odd count, type kept). A click on the chord that is far from the arc does not insert.

Not

• Not [visual-qa] EditVertex right-click add vertex on CIRCULARSTRING makes even control count #82 (parity of insert once a hit is found).
• Not [visual-qa] Ctrl-right-click delete on CIRCULARSTRING leaves a phantom point #97 (ctrl-right-click delete phantom).
• Not CompoundCurve member locater.

[grootstebozewolf]

PR #102: locater now hits 3-control arcs via CircularArcDensifier.nearestPointOnArc. Insert still splits that window (+2). Do not close without UX SIGN.