Mark dartdoc deprecated

Mark the `dartdoc` command as deprecated.
It's being replaced by the `dart doc` command.

Part of https://github.com/dart-lang/sdk/issues/44610

Change-Id: Ia0607cb53ef526388a749acb735fd6145149334e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/221948
Reviewed-by: Samuel Rawlins <srawlins@google.com>
Commit-Queue: Michael Thomsen <mit@google.com>

CHANGELOG.md

@@ -25,6 +25,15 @@
 
 [an issue]: https://github.com/dart-lang/sdk/issues/new
 
+- **Breaking Change** [#46100](https://github.com/dart-lang/sdk/issues/46100):
+  The standalone `dartdoc` tool has been
+  marked deprecated as previously announced.
+  Its replacement is the `dart doc` command.
+  Should you find any issues, or missing features, in the replacement
+  command, kindly file [an issue][].
+
+[an issue]: https://github.com/dart-lang/sdk/issues/new
+
 #### Linter
 
 Updated the Linter to `1.15.0`, which includes changes that

sdk/bin/dartdoc

@@ -3,6 +3,8 @@
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
+echo "Warning: 'dartdoc' is deprecated. Please use 'dart doc'." 1>&2
+
 function follow_links() {
   file="$1"
   while [ -h "$file" ]; do

sdk/bin/dartdoc.bat

@@ -3,6 +3,8 @@ REM Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 REM for details. All rights reserved. Use of this source code is governed by a
 REM BSD-style license that can be found in the LICENSE file.
 
+echo Warning: 'dartdoc' is deprecated. Please use 'dart doc'. 1>&2
+
 setlocal
 rem Handle the case where dart-sdk/bin has been symlinked to.
 set DIR_NAME_WITH_SLASH=%~dp0