Add EscapeStringOptions and escapeString tests

Change-Id: I86ead2f969c9e03c9edfa51bbc92ee06393fd7d6

src/libexpr/print.cc

@@ -198,12 +198,14 @@ private:
 
     void printString(Value & v)
     {
-        // NB: Non-printing characters won't be escaped.
         escapeString(
             output,
             v.string.s,
-            options.maxStringLength,
-            options.ansiColors
+            {
+                .maxLength = options.maxStringLength,
+                .outputAnsiColors = options.ansiColors,
+                // NB: Non-printing characters won't be escaped.
+            }
         );
     }