engine: look dictionaries up synchronously

The dictionary thread ran in imthread's own proc, so a lookup could
only start once the engine blocked, and it was a trie probe anyway; the
emoji and Hanja searches already called dictlookup directly. The
request/result channels, sequence numbers, staleness checks and the
second draw per Japanese key are gone; dictqjp fills the candidates
in place. Emit.dict and Lang.dictq only ever triggered lookups for
Vietnamese, which has no dictionary. dictlookup(Lang*, key, out, max)
returns the count. The Hanja lookup no longer pre-checks for a single
syllable; a reading either has an entry or it does not.

tests/trie_test.c

@@ -99,13 +99,12 @@ transmap_states(struct ct *t)
 		int eat;
 		char *emit;
 		char *next;
-		char *mapped;
 	} cases[] = {
-		{ "", 'k', 1, "", "k", "" },
-		{ "k", 'a', 1, "", "ka", "か" },
-		{ "ka", 's', 1, "か", "s", "" },
-		{ "ka", 'q', 0, "か", "", "" },
-		{ "k", 'q', 0, "k", "", "" },
+		{ "", 'k', 1, "", "k" },
+		{ "k", 'a', 1, "", "ka" },
+		{ "ka", 's', 1, "か", "s" },
+		{ "ka", 'q', 0, "か", "" },
+		{ "k", 'q', 0, "k", "" },
 	};
 	Emit e;
 	Im state;
@@ -125,7 +124,6 @@ transmap_states(struct ct *t)
 				i, cases[i].eat, e.eat);
 		checkstr(t, "emit", cases[i].emit, &e.s);
 		checkstr(t, "next", cases[i].next, &e.next);
-		checkstr(t, "mapped", cases[i].mapped, &e.dict);
 	}
 	trieclose(fixture);
 	state.l->map = saved;