Bump dartdoc to null safety

Change-Id: I30647c2ffaf9703f8356c9d3c2dadc13885b220d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/227960
Auto-Submit: Samuel Rawlins <srawlins@google.com>
Reviewed-by: Devon Carew <devoncarew@google.com>
Reviewed-by: Ben Konyi <bkonyi@google.com>
Commit-Queue: Ben Konyi <bkonyi@google.com>

.dart_tool/package_config.json

@@ -11,7 +11,7 @@
     "constraint, update this by running tools/generate_package_config.dart."
   ],
   "configVersion": 2,
-  "generated": "2022-01-12T18:31:13.380991",
+  "generated": "2022-01-12T18:16:46.198227",
   "generator": "tools/generate_package_config.dart",
   "packages": [
     {
@@ -250,7 +250,7 @@
       "name": "dartdoc",
       "rootUri": "../third_party/pkg/dartdoc",
       "packageUri": "lib/",
-      "languageVersion": "2.11"
+      "languageVersion": "2.14"
     },
     {
       "name": "dds",

DEPS

@@ -109,7 +109,7 @@ vars = {
   # For more details, see https://github.com/dart-lang/sdk/issues/30164
   "dart_style_rev": "08b0294d0a500d5c02168ef57dcb8868d0c3cb48",
 
-  "dartdoc_rev" : "66ee9a81b3bab35adcda18274b7d69567c98c3c6",
+  "dartdoc_rev" : "f9cfab1b84176873c80b89e7c8b54c669344f9ed",
   "devtools_rev" : "85932bb66aa782c4b2c528be7718960bf256ffb7",
   "ffi_rev": "4dd32429880a57b64edaf54c9d5af8a9fa9a4ffb",
   "fixnum_rev": "848341f061359ef7ddc0cad472c2ecbb036b28ac",