NcRichContenteditable: fix IME support on Mac OSX

[ShGKme]

☑️ Resolves

Confirm entering during composition session in IME on Mac OSX is considered by <NcRichContenteditable> as Enter and emits submit during the input.

Reproducible on Safari and Chromium on Mac.
Not reproducible on Linux or Windows.

• Related issues:
  • [Bug]: When using Zhuyin input method, the message will send out directly, I can't choose the word first.  nextcloud/spreed#9145
  • Enter and Shift+Enter for the send key in Chat function. nextcloud/spreed#3268

🖼️ Screenshots

🏚️ Before	🏡 After

🚧 Tasks

• Add detection of composition session
• Ignore Enter in composition session
• Add test for this case and some other basic unit tests

🏁 Checklist

• ⛑️ Tests are included or are not applicable
• 📘 Component documentation has been extended, updated or is not applicable

[Antreesy]

Can't test it properly on Linux, but according to MDN docs composition listeners seem legit to use. Tests are also look good from the code

[ShGKme]

Rebased onto master with conflict resolve and test assert uncomment

[ShGKme]

Just rebased onto master before merge, no changes.

[ShGKme]

/backport to stable7

[backportbot-nextcloud]

The backport to stable7 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable7
git pull origin stable7

# Create the new backport branch
git checkout -b fix/foo-stable7

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts. Resolve them.
git cherry-pick abc123

# Push the cherry pick commit to the remote repository and open a pull request
git push origin fix/foo-stable7

More info at https://docs.nextcloud.com/server/latest/developer_manual/getting_started/development_process.html#manual-backport