Upgrade: private-dictionary should be copied across to new prefs directory

### Description

The **private-dictionary-_locale_** file in the preferences directory holds spelling dictionary additions not associated with any specific project (as far as I can tell), but it fails to get copied across during version updates.

### Use case/motivation

Currently each time a version update occurs, heaps of spelling issues resurface. This would make updates more seamlessly retain workflow status quo.

### Related issues

_No response_

### Are you willing to submit a pull request?

No

Search the NetBeans code for private-dictionary-_locale_ and trace the preferences-directory migration performed during version updates. Verify the behavior with the relevant migration or preferences tests, and consider the work done when the dictionary file is retained in the new preferences directory after an update.

Written by the indexing model from the issue text.