To reproduce:
1. Create a new project
2. Open build settings window
3. Minimize Editor using the taskbar icon

Expected: Editor minimizes with all of its undocked windows
Actual: The Build Settings window remain not minimized

Reproduced with: 2017.4.35f1, 2018.4.16f1, 2019.3.0b1, 2019.3.0b6, 2019.3.0b12, 2019.3.0f6, 2020.1.0a22

Notes:
Linux minimizes all windows regardless of where they were opened from;
Mac minimizes only the focused window, regardless of where it was opened from;