Switch on the enhanced reference lookup system (#2705)

* It 'works' but no tests for new functionality yet

* dartfmt

* add tests for type parameters, handle more constructor parameter edge cases

* dartfmt rebuild

* remove debugging

* correct isEquivalentTo to handle element type forwarding

* The big switch

* This was never correct, delete hrefs for type parameters

* Correct a problem with inherited docs

* Remember, we need both

* Correct remaining SDK issues

* add a fully qualified name for DefinedElementType so that the comparison messages are more useful

* Remove commented out code block

* Stabilize the global table insertion order in the new lookup code.

* Keep using all packages -- might be necessary in some cases and I've done all my testing that way so far.

* Make byName more stable via hashCode.

* No need to rename it

Author: jcollins-g

lib/src/dartdoc_options.dart

@@ -1426,7 +1426,7 @@ Future<List<DartdocOption<Object>>> createDartdocOptions(
     DartdocOptionArgOnly<List<String>>('excludePackages', [], resourceProvider,
         help: 'Package names to ignore.', splitCommas: true),
     DartdocOptionArgFile<bool>(
-        'enhancedReferenceLookup', false, resourceProvider,
+        'enhancedReferenceLookup', true, resourceProvider,
         hide: true,
         help:
             'Use the new comment reference lookup system instead of the legacy '