How to reproduce:
1. Create a new project
2. Open Package Manager window
3. Try to resize it

Expected results: The resize cursor handle appears when hovering on the edge of the window, indicating that you can now resize
Actual results: The resize cursor handle never appears

Reproducible with 2017.4.32f1, 2018.4.10f1, 2019.2.8f1, 2019.3.0b6, 2020.1.0a8

Notes:
- The threshold at which you can resize the window is a little off - when clicking and dragging on the actual edge of the window, nothing happens. You need to click and drag a little bit towards the window for the resizing to happen
- On earlier versions, the resize cursor handle appears on some windows (the Package Manager window seems to always have this issue)