Bump dartdoc to 80c6f18f34b387d4b9ce89ddd2e3049093335f9d

Changes:
```
> git log --format="%C(auto) %h %s" 5df03dd..80c6f18
 https://dart.googlesource.com/dartdoc.git/+/80c6f18f Bump to 8.2.1 (3902)
 https://dart.googlesource.com/dartdoc.git/+/2d829875 update test expectations (3903)
 https://dart.googlesource.com/dartdoc.git/+/fa3a351c Privatize GetterSetterCombo.constantInitializer (3898)
 https://dart.googlesource.com/dartdoc.git/+/5c114a9c update test expectation for newer versions of package:args (3901)
 https://dart.googlesource.com/dartdoc.git/+/9d9b00c3 Require analyzer 6.10.0, stop using deprecated properties of LibraryElement. (3899)

```

Diff: https://dart.googlesource.com/dartdoc.git/+/5df03dd913a0a2e20421cac61112aa84111160e0..80c6f18f34b387d4b9ce89ddd2e3049093335f9d/
Change-Id: Ibffd0f08337ec63418bbf02d699d0f196702aed2
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/389220
Auto-Submit: Devon Carew <[email protected]>
Reviewed-by: Samuel Rawlins <[email protected]>
Commit-Queue: Samuel Rawlins <[email protected]>
Reviewed-by: Nate Bosch <[email protected]>

Author: devoncarew

DEPS

@@ -144,7 +144,7 @@ vars = {
   #
   # For more details, see https://github.com/dart-lang/sdk/issues/30164.
   "dart_style_rev": "5d35f4d829ffb8532d345d95d3e9504ae6cd839e", # disable tools/rev_sdk_deps.dart
-  "dartdoc_rev": "5df03dd913a0a2e20421cac61112aa84111160e0",
+  "dartdoc_rev": "80c6f18f34b387d4b9ce89ddd2e3049093335f9d",
   "ecosystem_rev": "2d58550f9e3fd8ecbc3b2e4444095fcb204a66c6",
   "file_rev": "6842feaef1c4e06239bd30f8d3ef722838b1c97e",
   "fixnum_rev": "83293b8ed86ccd574a94fcf4a2da43f31c1b43e0",