Fix: Pasting from excel inserts an image instead of a formatted table

[hiobjan]

📝 Summary

• Resolves: Pasting from excel inserts an image instead of a formatted table #8472

Added a check if the pasted content contains a table, either in HTML or TSV-like format. If so, let the regular paste pipeline handle it.

🖼️ Screenshots

🏚️ Before	🏡 After
B	A

🚧 TODO

• ...

🏁 Checklist

• Code is properly formatted (npm run lint / npm run stylelint / composer run cs:check)
• Sign-off message is added to all commits
• Tests (unit, integration and/or end-to-end) passing and the changes are covered with tests
• Documentation (README or documentation) has been updated or is not required

🤖 AI (if applicable)

• The content of this PR was partly or fully generated using AI tools
• The AI-generated content was reviewed, comprehended and tested by a human

[mejo-]

Thanks a lot @hiobjan for the contribution, much appreciated. The code changes look good to me. I have one comment, but it's not blocking.

The failing Playwright test is unrelated, you can ignore it.

To put the PR into a mergeable state, can you please do the following:

• squash all commits into one commit. https://stackoverflow.com/questions/1657017/how-to-squash-all-git-commits-into-one describes how to do that.
• given that the code changes were assisted by AI, make sure the commit message contains the Assisted-By footer, as described in our AI Policy. You can add the trailer for the last Git commit with git commit --amend --trailer "Assisted-by: AGENT_NAME:MODEL_VERSION"

[mejo-]

I wonder whether we should let the regular paste pipeline handle it whenever HTML or text paste data is non-empty, but I'm not sure here. Do others have knowledge here and have an opinion on whether this is a good idea @max-nextcloud @skjnldsv @susnux @ShGKme?

To give some context: the handlePaste function here takes care of inserting pasted images. Unfortunately, copying data from Microsoft Excel will put a screenshot of the copied data into event.clipboardData.files, I guess to ensure compatibility with pasting the copied content into places that cannot deal with the table data.

[mejo-]

Thanks a lot again! I tested it now and it works as expected 🚀

[mejo-]

/backport to stable34

[mejo-]

/backport to stable33