Complete rebranding of bibtexkey as citationkey

[tobiasdiez]

Follow-up from #6545.

• Change in CHANGELOG.md described (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.

[koppor]

The JabRef maintainers will add the following name to the AUTHORS file. In case you want to use a different one, please comment here and adjust your name in your git configuration for future commits.

MLEP

[tobiasdiez]

Migration of preferences etc is not necessary because we have such a beautiful architecture that every field name is passed trough here. 😆 😄

[Siedlerchr]

In general looks good, but I would prefer a preferences migration for the preview and the default patterns etc to be consistent. Otherwise it looks confusing when we always refer to citation key but some pieces still use bibtexkey
Did you test if custom layout files still work with \bibtexkey ?

[Siedlerchr]

Please test if the layout files still work and follow the checklist.

[tobiasdiez]

I left the bibtexkey in the old version of the migration tests since this is the form they are encountered usually for a user, so the tests are really covering the use case.

The custom layout files I didn't check, but with custom preview it did worked.

[calixtus]

We should merge this soon, so conflicts with new PRs can be avoided. I scrolled through this one, but did not see anything.

[tobiasdiez]

Agreed. Let's merge it now, and hopefully everything keeps working. If not, feel free to assign the new issues on my name ;-)

[Siedlerchr]

There are failing tests related to the Preferences MIgration:
https://github.com/JabRef/jabref/runs/1086155398

jabRefPreferences.setPreviewStyle(
    "<font face="sans-serif"><b><i>\bibtextype</i><a name="\citationkey">\begin{citationkey} (\citationkey)</a>\end{citationkey}</b><br>__NEWLINE__\begin{author} \format[Authors(LastFirst,Initials,Semicolon,Amp),HTMLChars]{\author}<BR>\end{author}__NEWLINE__\begin{editor} \format[Authors(LastFirst,Initials,Semicolon,Amp),HTMLChars]{\editor} <i>(\format[IfPlural(Eds.,Ed.)]{\editor})</i><BR>\end{editor}__NEWLINE__\begin{title} \format[HTMLChars]{\title} \end{title}<BR>__NEWLINE__\begin{chapter} \format[HTMLChars]{\chapter}<BR>\end{chapter}__NEWLINE__\begin{journal} <em>\format[HTMLChars]{\journal}, </em>\end{journal}__NEWLINE__\begin{booktitle} <em>\format[HTMLChars]{\booktitle}, </em>\end{booktitle}__NEWLINE__\begin{school} <em>\format[HTMLChars]{\school}, </em>\end{school}__NEWLINE__\begin{institution} <em>\format[HTMLChars]{\institution}, </em>\end{institution}__NEWLINE__\begin{publisher} <em>\format[HTMLChars]{\publisher}, </em>\end{publisher}__NEWLINE__\begin{year}<b>\year</b>\end{year}\begin{volume}<i>, \volume</i>\end{volume}\begin{pages}, \format[FormatPagesForHTML]{\pages} \end{pages}__NEWLINE__\begin{abstract}<BR><BR><b>Abstract: </b> \format[HTMLChars]{\abstract} \end{abstract}__NEWLINE__\begin{comment}<BR><BR><b>Comment: </b> \format[Markdown,HTMLChars]{\comment} \end{comment}</dd>__NEWLINE__<p></p></font>"
);
-> at org.jabref.migrations.PreferencesMigrationsTest.upgradePreviewStyleAllowMarkupDefault(PreferencesMigrationsTest.java:169)
Actual invocations have different arguments:
jabRefPreferences.setPreviewStyle(
    "<font face="sans-serif"><b><i>\bibtextype</i><a name="\bibtexkey">\begin{bibtexkey} (\bibtexkey)</a>\end{bibtexkey}</b><br>__NEWLINE__\begin{author} \format[Authors(LastFirst,Initials,Semicolon,Amp),HTMLChars]{\author}<BR>\end{author}__NEWLINE__\begin{editor} \format[Authors(LastFirst,Initials,Semicolon,Amp),HTMLChars]{\editor} <i>(\format[IfPlural(Eds.,Ed.)]{\editor})</i><BR>\end{editor}__NEWLINE__\begin{title} \format[HTMLChars]{\title} \end{title}<BR>__NEWLINE__\begin{chapter} \format[HTMLChars]{\chapter}<BR>\end{chapter}__NEWLINE__\begin{journal} <em>\format[HTMLChars]{\journal}, </em>\end{journal}__NEWLINE__\begin{booktitle} <em>\format[HTMLChars]{\booktitle}, </em>\end{booktitle}__NEWLINE__\begin{school} <em>\format[HTMLChars]{\school}, </em>\end{school}__NEWLINE__\begin{institution} <em>\format[HTMLChars]{\institution}, </em>\end{institution}__NEWLINE__\begin{publisher} <em>\format[HTMLChars]{\publisher}, </em>\end{publisher}__NEWLINE__\begin{year}<b>\year</b>\end{year}\begin{volume}<i>, \volume</i>\end{volume}\begin{pages}, \format[FormatPagesForHTML]{\pages} \end{pages}__NEWLINE__\begin{abstract}<BR><BR><b>Abstract: </b> \format[HTMLChars]{\abstract} \end{abstract}__NEWLINE__\begin{comment}<BR><BR><b>Comment: </b> \format[HTMLChars]{\comment} \end{comment}</dd>__NEWLINE__<p></p></font>"
);
-> at org.jabref.migrations.PreferencesMigrationsTest.upgradePreviewStyleAllowMarkupDefault(PreferencesMigrationsTest.java:164)
jabRefPreferences.getPreviewStyle(