NB15 problem adding libraries to project in the Properties>Libraries dialog box

### Apache NetBeans version

Apache NetBeans 15 release candidate

### What happened

In the Project Properties>Libraries dialog box (Ant Java project), after adding a certain number of libraires (somewhere around 5-7), the “+” signs for adding things to Modulepath and Classpath disappear. It seems that they will come back if enough libraries are deleted. When the “+” signs have disappeared, one can still add libraries by right-clicking “Libraries” in the Projects tree. These buttons should not disappear no matter how full the window gets. I am upgrading from NB 8.2 to NB 15, so I don't know precisely know when this bug was introduced, as NB 8.2 had a different dialog box layout.

### How to reproduce

1. Project Properties>Libraries dialog box for an Ant Java project
2. Click "+" sign to add a library.
3. Continue to add libraries, and the "+" sign will disappear
4.

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

Apache NetBeans 12.3 or earlier

### Operating System

Windows 10 Professional

### JDK

Java(TM) SE Runtime Environment (build 17+35-LTS-2724)

### Apache NetBeans packaging

Apache NetBeans binary zip

### Anything else

Problem occurs regularly.

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

No

### Code of Conduct

Yes

Start in the Project Properties > Libraries dialog for an Ant Java project and reproduce the issue by adding several libraries until the Modulepath and Classpath “+” buttons disappear. Trace the dialog’s layout behavior and compare it with the alternative library-adding action; done means both buttons remain available as libraries are added.

Written by the indexing model from the issue text.