M6: the .fig export names the case of a multi-line instance text on its main's text path (#2323)

An override can't take its layer off the main component's text path, so an instance text of more than one line, whose main is on a path, stays on that path in the file. The export warned the general instance mismatch for it. It now says exactly that case: "an instance's text of more than one line stays on its main component's text path in the file, as an override can't take it off". FigCraft's own import reads such a layer as plain text. The docs' Left out list names the case.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Model-Effort: Opus 5.5 drove and wrote

docs/file-format-parity.md

@@ -141,7 +141,7 @@ scales and empty-style clears; they have not been checked in other software.
   with the width on both sides when the shape has a fill too), pattern fills, WebP export settings (written as PNG),
   image adjustments, glass settings other than frost, springs other than Gentle (written as ease
   out), set-variable, set-variable-mode and conditional actions, scroll-to offsets, text decoration
-  looks, variable font axes, text on a path with more than one line or on a path the format can't hold (written as plain text), the parts of a text's path after the first, text on a path in an instance but not in its main or the other way round (written as the main has it), nested list levels, OpenType features, per-layer operations inside boolean groups, different stroke ends
+  looks, variable font axes, text on a path with more than one line or on a path the format can't hold (written as plain text), the parts of a text's path after the first, text on a path in an instance but not in its main or the other way round (written as the main has it), an instance's text of more than one line on a main on a path (it stays on that path, as an override can't take it off), nested list levels, OpenType features, per-layer operations inside boolean groups, different stroke ends
   on lines, the Dash cap (no public name for it). Not written at all: stroke outlines of dashed and per-side strokes and of inside or
   outside strokes on polygons, stars and vectors, glyph outlines of text (a reader lays text out
   with its own fonts), version history and branches.