UI Builders Library section does not show package UI components when the "Show Package Files" field is checked

How to reproduce:

1. Open the “EmptyProject.zip“ project
2. Open UI Builder (Window > UI Toolkit > UI Builder)
3. To the right of the “Library” section press the three vertical dots
4. Check the “Show Package Files“ button
5. Observe the Library section

Expected results: All package components are visible alongside the built-in UI components in the Library section
Actual results: Package components are not visible in the Library section

Reproducible in: 2021.3.34f1, 2022.3.17f1, 2023.2.6f1, 2023.3.0b2

Reproduced on: Windows 11 Pro, macOS 13.5.2 (M1, 2020)
Not reproduced on: No other environment tested

Note: The project uses the App UI package (com.unity.dt.app-ui)