feat(suggestion): add option to allow triggering chars to also be in suggestions

[tcitworld]

Please describe your changes

It's currently not possible to mention emails or federated usernames for instance, because the triggering char (often @) cannot be included in the mention suggestion itself. This option allows to have some, so that the mention will only end with a space. That makes it incompatible with the allowSpaces option.

How did you accomplish your changes

Added the option in question and modified the regex matching the suggestion text to use it.

How have you tested your changes

Tested that the new regex will also include the part after a secondary triggering character.

How can we verify your changes

Add allowToIncludeChar to the suggestion settings, then type an email as suggestion.

Remarks

[add any additional remarks here]

Checklist

• [x] The changes are not breaking the editor
• [ ] Added tests where possible
• [x] Followed the guidelines
• [x] Fixed linting issues

Related issues

Closes #4447

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[bdbch]

Moved this into #5895

[tcitworld]

Thanks !