unicode escapes in property files are converted to lowercase

### Apache NetBeans version

Apache NetBeans 13

### What happened

when saving properties with unicode escapes, they are all converted to lowercase. it is very old issue (https://bz.apache.org/netbeans/show_bug.cgi?id=239513), please fix it since it makes huge mess in git

### How to reproduce

open any .properties file with uppercase unicode escapes e.g.

date.yesterday=v\u010Dera

and save it. the property value gets converted to:

date.yesterday=v\u010dera

### Did this work correctly in an earlier version?

No

### Operating System

Microsoft Windows [Version 10.0.19044.1586]

### JDK

Java(TM) SE Runtime Environment 11.0.11+9-LTS-194

### Apache NetBeans packaging

Apache NetBeans provided installer

### Anything else

_No response_

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

No

### Code of Conduct

Yes

Reproduce the issue in the NetBeans properties editor using a .properties value such as v\u010Dera, then trace the save path that converts Unicode escapes. Done means saving the file preserves the uppercase escape as \u010D rather than changing it to \u010D with a lowercase hexadecimal digit; add or update a regression test if the relevant test location is found.

Written by the indexing model from the issue text.