Desktop Linux runtime does not respect -popupwindow command line argument

Steps to reproduce:

1. Build an empty project for Desktop or Embedded Linux
2. Run the Embedded or Desktop Linux Player with -popupwindow command line arg:
   1. ./LinuxPlayer -popupwindow

Actual results: 

• LinuxPlayer window in windowed mode is not borderless when the argument is passed

Expected results: 

• LinuxPlayer window in windowed mode is borderless when the argument is passed

Reproducible with versions: 

• All Desktop and Embedded Linux runtime versions

Not reproducible with versions: 

• N/A

Can’t test with versions: 

• N/A

Tested on (OS): 

• Ubuntu 24.04.2 LTS

Notes:

• Slack thread: https://unity.slack.com/archives/C06TQC2DA/p1747160504888839