Optimize splitting lines with many rules.

lib/src/line_splitting/line_splitter.dart

Index: lib/src/line_splitting/line_splitter.dart
diff --git a/lib/src/line_splitting/line_splitter.dart b/lib/src/line_splitting/line_splitter.dart
index f562ca40dc699dc45f96e404f1b4ae7c2b66d207..78aa54dc7d17078382643c894d62eac2ecd2af6e 100644
--- a/lib/src/line_splitting/line_splitter.dart
+++ b/lib/src/line_splitting/line_splitter.dart
@@ -145,6 +145,12 @@ class LineSplitter {
     for (var i = 0; i < rules.length; i++) {
       rules[i].index = i;
     }
+
+    // Now that every used rule has an index, tell the rules to discard any
+    // constraints on unindexed rules.
+    for (var rule in rules) {
+      rule.forgetUnusedRules();
+    }
   }
 
   /// Determine the best way to split the chunks into lines that fit in the