Give the possability to use a Cross/X to check a PDCheckBox

[Backfisch145]

Is your feature request related to a problem? Please describe. In our usecase, we want to be able to use an X instead of a check, to mark a PDCheckBox as checked.

Describe the solution you'd like It would be perfect if you could use a function like .checkCross() or something like that, that draws an X instead of a check

Check the type of feature request:

• [ ] Feature available in a newer PDFBox desktop version
• [ ] Feature not yet ported to PdfBox-Android
• [x] Other

Additional context None

[THausherr]

See the CreateCheckBox.java example in PDFBox for desktop. The cross would be done by calling appearanceCharacteristics.setNormalCaption("4");.