Bump ai to 3d3b7fdaddead83ce262377e5c4ce5b2a843066c

Also updates manage_deps.dart to handle trailing slashes.

Changes:
```
> git log --format="%C(auto) %h %s" 07df396..3d3b7fd
 https://dart.googlesource.com/ai.git/+/3d3b7fd Enable roots tools always, collapse under one tool (440)

```

Diff: https://dart.googlesource.com/ai.git/+/f1cddc8e1905b9a5753a93ce451522e564311251..3d3b7fdaddead83ce262377e5c4ce5b2a843066c/
Change-Id: Ia09061667c3e5f8642a45d6fd491143ac80556c5
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/495060
Reviewed-by: Sigmund Cherem <sigmund@google.com>
Commit-Queue: Sigmund Cherem <sigmund@google.com>
Commit-Queue: Jake Macdonald <jakemac@google.com>
Auto-Submit: Jake Macdonald <jakemac@google.com>

DEPS

@@ -134,7 +134,7 @@ vars = {
   ### /third_party/pkg dependencies
   # 'tools/rev_sdk_deps.dart' will rev pkg dependencies to their latest; put an
   # EOL comment after a dependency to instead pin at the current revision.
-  "ai_rev": "07df396bdb15cb52edbe59b4bc2c5648c2203781",
+  "ai_rev": "3d3b7fdaddead83ce262377e5c4ce5b2a843066c",
   "core_rev": "347df4b546f315fc1ff69c6e65f2a023b0263b1d",
   "dartdoc_rev": "a57f497ae9df6e6073b5eb7ddf253d0b2eb470c3",
   "ecosystem_rev": "6b2164f8f57583a7bcaa32341eaa219efd8fd2d3",

tools/manage_deps.dart

@@ -72,7 +72,7 @@ This will:
       print('Note your git checkout is dirty!');
     }
 
-    final pkgDir = argResults.rest.first;
+    final pkgDir = p.normalize(argResults.rest.first);
     if (!Directory(pkgDir).existsSync()) {
       usageException('No directory $pkgDir');
     }