Brightness (FreeBSD): add support

I hope someone can test it

CMakeLists.txt

@@ -432,7 +432,7 @@ elseif(BSD)
         src/detection/bios/bios_bsd.c
         src/detection/bluetooth/bluetooth_linux.c
         src/detection/board/board_bsd.c
-        src/detection/brightness/brightness_nosupport.c
+        src/detection/brightness/brightness_bsd.c
         src/detection/chassis/chassis_bsd.c
         src/detection/cpu/cpu_bsd.c
         src/detection/cpuusage/cpuusage_bsd.c

src/detection/brightness/brightness_bsd.c

@@ -0,0 +1,47 @@
+#include "brightness.h"
+
+#if __has_include(<sys/backlight.h>)
+
+#include "common/io/io.h"
+
+#include <sys/backlight.h>
+#include <sys/ioctl.h>
+#include <sys/fcntl.h>
+#include <unistd.h>
+
+const char* ffDetectBrightness(FFlist* result)
+{
+    // https://man.freebsd.org/cgi/man.cgi?query=backlight&sektion=9
+    char path[] = "/dev/backlight/backlight0";
+
+    for (char i = '0'; i <= '9'; ++i)
+    {
+        path[sizeof(path) - 2] = i;
+
+        FF_AUTO_CLOSE_FD int blfd = open(path, O_RDONLY);
+        if (blfd < 0)
+            continue;
+
+        struct backlight_props status;
+        if(ioctl(blfd, BACKLIGHTGETSTATUS, &status) < 0)
+            continue;
+
+        FFBrightnessResult* display = (FFBrightnessResult*) ffListAdd(result);
+        ffStrbufInit(&display->name);
+        display->value = (float) status.brightness / BACKLIGHTMAXLEVELS;
+
+        struct backlight_info info;
+        if(ioctl(blfd, BACKLIGHTGETINFO, &info) < 0)
+            ffStrbufAppendS(&display->name, info.name);
+    }
+    return NULL;
+}
+
+#else
+
+const char* ffDetectBrightness(FF_MAYBE_UNUSED FFlist* result)
+{
+    return "Backlight is supported only on FreeBSD 13 and newer";
+}
+
+#endif