Write temporary file on bib import in jabrefhost.ps1

[reox]

This resolves an issue where the encoding somehow got lost when using
the Jabref Browser extension. It will now write a temporary file
with UTF-8 encoding rather than passing the bibtex on the commandline.

See JabRef/JabRef-Browser-Extension#274

• [] Change in CHANGELOG.md described in a way that is understandable for the average user (if applicable)
• [] Tests created for changes (if applicable)
• [] Manually tested changed features in running JabRef (always required)
• [] Screenshots added in PR description (for UI changes)
• [] Checked documentation: Is the information available and up to date? If not created an issue at https://github.com/JabRef/user-documentation/issues or, even better, submitted a pull request to the documentation repository.

[tobiasdiez]

Thanks!
Looks good to me. Could you please also add an entry in the changelog? Thanks.

For the record, this also fixes #7374.

[reox]

I put that under changed, is that OK?