The end-of-system barline and right margin must account for repeat-end / final barline glyph width, not a flat constant

A repeat-end barline (thin+thick line with dots) and a final barline are visually and dimensionally wider than an ordinary single barline; the right margin at a system's end must be large enough for whichever barline glyph will actually be drawn there.

`RIGHT_MARGIN = 10` (line 30) is a single flat constant used for every system regardless of barline type, while `repeatEnd` (line 893) is only applied `isLast` via `stave.setEndBarType(VF.Barline.type.REPEAT_END)` — a repeat-end barline is a wider glyph than the plain barline the constant was presumably tuned against, with no conditional widening of `RIGHT_MARGIN`/`canvasW` (line 831) when `repeatEnd && isLast`.

Gould, Behind Bars (barline types and their relative widths); Read, Music Notation (barline glyph specifications); Ross, The Art of Music Engraving (end-of-system margin conventions).

This rule can be decided from pitches, durations and voices — no layout required. A validator can check it before anything is drawn.