Implementation of new modifiers for issue #11367

[Mtjpp]

Describe the changes you have made here:

Implementation for issue: #11367

I have implemented new modifiers that can be used when renaming a PDF file used in file name format based on this comment: #11367 (comment) .

List of implemented modifiers:
Camel
CamelN
VeryShortTitle
ShortTitle

User documentation needs to be updated:
https://docs.jabref.org/setup/citationkeypatterns#modifiers

Mandatory checks

• I own the copyright of the code submitted and I licence it under the MIT license
• 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.

[koppor]

First impression: Looks good.

There should be tests for the use of veryhorttitle etc. I think, you will find the existing tests and then you can refine them.

[Mtjpp]

@koppor
Hello I have implemented unit tests can u review it please ?

[koppor]

You can remove the tests, because the functionality of the called formatters are already tested (otherwise, I need to tell you: use @ParameterizedTest, do not prefix tests with test_ and we would need another tough round here)

I am sorry that I wrote "I think, you will find the existing tests and then you can refine them.". Here is the pointer: Add before org.jabref.logic.citationkeypattern.BracketedPatternTest#expandBracketsWithAuthorStartingWithBrackets

1. Add a new @ParameterizedTest with @CsvSource. You see at other JabRef code how it works (use Ctrl+Shift+F).
2. Add tests for a variant of the cases mentioned at Special field markers and modifiers #11367 (comment). Use field TITLE instead of USER_CUSTOM_TITLE_FIELD.

[github-actions]

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