pkg/dartdoc: moving files around, fix library names

pkg/docgen/test/multi_library_code/lib/dottedLibraryName.dart

 library library.name.wiith.dots.init;
 
 /// This library is purely for testing purposes, to ensure
 /// that we have a library that has dots in its name and
 /// that it works properly
 ///
 /// In addition, it's nice to have something which has paragraph
 /// breaks inside a triple-slash doc comment.
 ///
 /// Like this.
@@ skipping 14 matching lines @@
 }
 
 /// This is another class.
 class AnotherClass {
   /// This method returns [List<int>] containing the number
   /// three three times. Compare with [SomeClass.someMethod].
   List<int> anotherMethod() {
     return const [3, 3, 3];
   }
 }