implement enhanced clipboard for html editor

[gtalha07]

Description:

Currently, appflowy_editor own clipboard APIs don't support handling rich text copy/paste. But interestingly, they have support in their parent repo which is built on flutter front-end and discovered very interesting package they've been using for handling formatted text and custom events: https://pub.dev/packages/super_clipboard.

The package itself relies on rust for low level functionality as they've described which is of course, efficient but also has a way of supporting custom json objects (imo can be very good for handling our acter objects inline). And not only handles events in-app but also supports receiving external events (like browser or another app). Although in some platforms, some might impose restrictions because of their nature but normally it works well as it's been previewed below.

PREVIEW:

Tested it with Firefox Browser and showcasing clipboard events receiving and sending:

Screen.Recording.2025-06-27.at.20.01.38.mov

General usage showcase:

(DESKTOP):

Screen.Recording.2025-06-27.at.20.17.45.mov

(MOBILE):

ScreenRecording_06-27-2025.21-35-33_1.MP4

[github-actions]

Hey there 👋,
and thanks for the contribution. But it seems like you forgot to

• 📰 Add a markdown file in .changes/ explaining what changed

[codecov]

Codecov Report

Attention: Patch coverage is 25.37313% with 100 lines in your changes missing coverage. Please review.

Project coverage is 46.68%. Comparing base (acb1c09) to head (990a0cf).

Files with missing lines	Patch %	Lines
...oolkit/html_editor/services/clipboard_service.dart	2.70%	36 Missing ⚠️
...ditor/clipboard/commands/custom_paste_command.dart	22.72%	34 Missing ⚠️
...editor/clipboard/commands/custom_copy_handler.dart	27.27%	16 Missing ⚠️
...pp/lib/common/toolkit/html_editor/html_editor.dart	65.38%	9 Missing ⚠️
.../features/chat_ng/actions/copy_message_action.dart	0.00%	3 Missing ⚠️
...atures/chat_ng/widgets/message_actions_widget.dart	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3150      +/-   ##
==========================================
- Coverage   46.75%   46.68%   -0.08%     
==========================================
  Files         948      951       +3     
  Lines       57819    57939     +120     
==========================================
+ Hits        27035    27049      +14     
- Misses      30784    30890     +106     

Flag	Coverage Δ
integration-test	58.01% <ø> (-0.06%)	⬇️
unittest	39.18% <25.37%> (-0.07%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.