TinyPilot can't send KEY_SWITCHVIDEOMODE

[mtlynch]

On some laptops, the laptop doesn't output the display to an external monitor unless the user presses the KEY_SWITCHVIDEOMODE key. On Dell laptops, this is Fn+F8:

I ran evtest to dump output from a Dell laptop's keyboard, and this was what I saw when I pressed Fn+F8:

Event: time 1644874377.083934, -------------- SYN_REPORT ------------
Event: time 1644874381.374129, type 4 (EV_MSC), code 4 (MSC_SCAN), value 8b
Event: time 1644874381.374129, type 1 (EV_KEY), code 227 (KEY_SWITCHVIDEOMODE), value 1
Event: time 1644874381.374129, -------------- SYN_REPORT ------------
Event: time 1644874381.374152, type 4 (EV_MSC), code 4 (MSC_SCAN), value 8b
Event: time 1644874381.374152, type 1 (EV_KEY), code 227 (KEY_SWITCHVIDEOMODE), value 0

Full logs: https://gist.github.com/mtlynch/8544fb605bb20cddf7b05ca0c98e1e2b#file-dell-xps-native-keyboard-log

So, the Fn+F8 combination maps to KEY_SWITCHVIDEOMODE, which has a code of 227 on the keyboard.

I tried evtest from the TinyPilot USB device, and KEY_SWITCHVIDEOMODE does not appear as a supported code: https://gist.github.com/mtlynch/8544fb605bb20cddf7b05ca0c98e1e2b#file-tinypilot-virtual-keyboard-log

I'm not sure if there's something we can change in the USB HID descriptor to support this code. It's possible that USB keyboards simply can't send KEY_SWITCHVIDEOMODE, because I don't see it documented in the USB HID spec.