MTEXT: Height, Justify, Line spacing, Rotation, Style, Width, Columns (part of #408) (#415)

The options at MTEXT's "Specify opposite corner" prompt printed "not
available yet". Each now asks its question and returns to the corner
prompt: Height (also sets TEXTSIZE), Justify (TL..BR, the insertion point
is the box's attachment point), Line spacing (At least/Exactly, then a
factor such as 1.5x or a distance), Rotation (picked, or typed through the
drawing's angle settings; the box turns with it), Style (? lists them),
Width (replaces the opposite corner) and Columns (No; Dynamic and Static
say columns are not available yet). MText stores the line spacing style
(DXF group 73) so Exactly round-trips.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

crates/render/src/tests.rs

@@ -284,6 +284,7 @@ fn truetype_mtext_and_dimension_text() {
             style: "Standard".into(),
             contents: "A{\\C1;B}\\P\\S1/2;".into(),
             line_spacing: 1.0,
+            line_spacing_exact: false,
         }),
     )
     .unwrap();