Fix issue with actions on empty space of menu items

[Clunphumb]

This change fixes #8388 by removing CustomMenuItem from several context menus. This also removes the corresponding tool tips.

The issue is illustrated in the following image:

For "Normalize to BibTeX name format" and every entry of the "Change case" menu you have to click inside the smaller red box to actually fire the event while you can click on the bigger red box for every other entry. This is caused by the usage of CustomMenuItem which shrinks the clickable box to the actual content. It is possible to add padding to the labels to enlarge the clickable area. However, given the dynamic nature of spacing in those menus I wasn't able to get acceptable results. This would increase future maintenance efforts as well because changes would always have to address CustomMenuItems and "normal" MenuItems.
Removing CustomMenuItems on the other hand would come at the price of removing tool tips as well. Given that almost all context menu entries aren't using tool tips, I would think that this wouldn't be a big problem.

This PR doesn't cause any visual changes as far as I can tell.

Please let me know what you think about this PR and thank you very much in advance!

Mandatory checks

• 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 developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
• Checked documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request to the documentation repository.

[Siedlerchr]

Thank you very much for the investigation! Sounds reaonsable to me to replace them with the normal entriex

[calixtus]

DevCall decision:

We think that this is a reasonable tradeoff, since we don't really know any other application which uses tooltips for context menu entries beside pure symbols.
E.g. in firefox:

Therefor we will merge this.

[calixtus]

Please fix the localization test, then we will merge.
Thank you for your efforts investigating and fixing this issue.

[Clunphumb]

Thank you for your feedback. I removed the unused key and squashed my commits.

[Siedlerchr]

LGTM

[Siedlerchr]

You don't need to squash your commits, this is done when we merge

[calixtus]

Please avoid force-pushing on GitHub, since comments on commits will loose it's link.

[calixtus]

Lgtm

[calixtus]

Can you please check the documentation, if the removed tooltips should or need to be somehow replaced by some note?

[Clunphumb]

An explanation of the entries is found under Save Actions.
Personally, I wouldn't look in this subsection for the information, but with the search this can be found easily. I think there are no changes necessary in the documentation.