KMSDRM/EVDEV: add VT switching support for FreeBSD

[Defenso-QTH]

Description

This PR adds support for VT switching when using KMSDRM in FreeBSD.

Closes #14298

Existing Issue(s)

SDL3 uses /dev/input/event* evdev devices to get input, so these devices need to be readable to the user. It means that the user, and the SDL, can read all events from input devices, including for instance passwords input in other VTs after switching.

In this PR, the SDL simply ignores this content instead of passing it to the application, but for a secure solution, a seat management solution will be necessary. The SDL side could be implemented using libseat which offers compatibility with both seatd and (e)logind.

Testing

Done

• Tested on FreeBSD 14.3-RELEASE-p5.
• With applications with FreeRDP 3.17.2 and Ymir 0.2.0.
• No leaking to underlying text terminal.
• No input in other VTs ends up in the SDL application.

To-do

• Test on Linux
• Other applications?

[slouken]

This PR failed CI on FreeBSD:

/home/runner/work/SDL/SDL/src/core/freebsd/SDL_evdev_kbd_freebsd.c:340:11: error: unused variable 'devicePath' [-Werror,-Wunused-variable]
  340 |     char *devicePath;
      |           ^~~~~~~~~~
1 error generated.

[Defenso-QTH]

Sorry, I forgot that one when filtering out debug comments.

[slouken]

Merged, thanks!