test(typesetters): Add test case for speaker changes in dialogues

tests/feat-emdash-dialogue.expected

@@ -0,0 +1,70 @@
+Set paper size 	209.7637818	297.6377985
+Begin page
+Mx 	10.4882
+My 	31.5323
+Set font 	Gentium Plus;22;400;;normal;;;LTR
+T	179 w=16.8545	(—)
+Mx 	33.1564
+T	47 82 85 72 80 w=58.0830	(Lorem)
+Mx 	102.5788
+T	76 83 86 88 80 w=55.4404	(ipsum)
+Mx 	169.3586
+T	71 82 w=22.5049	(do)
+Mx 	191.8635
+T	16 w=7.4121	(-)
+Mx 	10.4882
+My 	57.9323
+T	79 82 85 w=25.7383	(lor)
+Mx 	49.1531
+T	86 76 87 w=22.0322	(sit)
+Mx 	71.1853
+T	17 w=5.0381	(.)
+Mx 	89.1500
+T	179 w=16.8545	(—)
+Mx 	118.9310
+T	54 72 71 w=32.0762	(Sed)
+Mx 	163.9338
+T	81 82 81 w=35.3418	(non)
+Mx 	10.4882
+My 	84.3323
+T	85 76 86 88 86 w=43.3232	(risus)
+Mx 	53.8114
+T	17 w=5.0381	(.)
+Mx 	10.4882
+My 	110.7323
+T	179 w=16.8545	(—)
+Mx 	33.1564
+T	49 82 81 w=37.4795	(Non)
+Mx 	70.6358
+T	17 w=5.0381	(.)
+Mx 	10.4882
+My 	137.1323
+T	179 w=16.8545	(—)
+Mx 	36.8402
+T	47 82 85 72 80 w=58.0830	(Lorem)
+Mx 	104.4207
+T	76 83 86 88 80 w=55.4404	(ipsum)
+Mx 	169.3586
+T	71 82 w=22.5049	(do)
+Mx 	191.8635
+T	16 w=7.4121	(-)
+Mx 	10.4882
+My 	163.5323
+T	79 82 85 w=25.7383	(lor)
+Mx 	49.1531
+T	86 76 87 w=22.0322	(sit)
+Mx 	71.1853
+T	17 w=5.0381	(.)
+Mx 	89.1500
+T	179 w=16.8545	(—)
+Mx 	118.9310
+T	54 72 71 w=32.0762	(Sed)
+Mx 	163.9338
+T	81 82 81 w=35.3418	(non)
+Mx 	10.4882
+My 	189.9323
+T	85 76 86 88 86 w=43.3232	(risus)
+Mx 	53.8114
+T	17 w=5.0381	(.)
+End page
+Finish

tests/feat-emdash-dialogue.sil

@@ -0,0 +1,16 @@
+\begin[papersize=a7]{document}
+\nofolios
+\neverindent
+\font[size=22pt]
+\set[parameter=linebreak.emergencyStretch, value=50pt]
+
+% Affect paragraph-leading em-dash but not later...
+— Lorem ipsum dolor sit. — Sed non risus.
+
+— Non.
+
+\set[parameter=typesetter.fixedSpacingAfterInitialEmdash, value=false]
+
+— Lorem ipsum dolor sit. — Sed non risus.
+
+\end{document}