Make `ISSNCleanup` a `Formatter`

[koppor]

JabRef allows for fixing field content. Example: Use only one space instead of multiple ones in a field. These is called "formatters" in JabRef.

Example: org.jabref.logic.formatter.bibtexfields.NormalizeWhitespaceFormatter

The class org.jabref.logic.cleanup.ISSNCleanup is such a formatter, but its implemetned as Cleanup. Which is wrong. --> CleanUps are used for multi-field operations.

Task

1. Move org.jabref.logic.cleanup.ISSNCleanup to package org.jabref.logic.formatter.bibtexfields
2. Rename to NormalizeIssn
3. Make it extends Formatter (remove implements CleanupJob)
4. Adapt code accordingly

• Remove from "Miscallenous" section in cleanup dialog
• Add the formatter to org.jabref.logic.cleanup.FieldFormatterCleanups#DEFAULT_SAVE_ACTIONS (only for field org.jabref.model.entry.field.StandardField#ISSN)

Micro task:

Fix formatting in jabgui/src/main/resources/org/jabref/gui/cleanup/CleanupPresetPanel.fxml - the indent is wrong. (from line 48 on)

---

This is a follow-up to #1590.

[siddhantkore]

\assign-me

[github-actions]

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