No longer possible to enter the Magic SysRq key combination

Description

It isn't possible to use the Magic SysRq key combination on the TinyPilot keyboard. This appears to be a regression as this functionality was previously added and then subsequently lost during a refactor.

What's the behavior that you expect?

• The "SysRq" key should still be labeled on the TinyPilot keyboard.
• Pressing "SysRq" (or the equivalent "Print" key) shouldn't end the combination if the "Alt" modifier is already pressed.

What's happening instead?

• The "SysRq" key is no longer labelled on the TinyPilot keyboard.
• Pressing the equivalent "Print" key cancels the "Alt" modifier and so the combination can't be completed.

What are the steps to reproduce this behavior?

1. Connect a TinyPilot device to a Linux system and open the interface in Chrome.
2. Attempt to display the help text by pressing "Alt"+"SysRq"/"Print"+"h".
3. Note that the combination ends before "h" can be pressed.

Screenshots

N/A

Logs

N/A

Reproduce the combination in Chrome on a TinyPilot device using the steps in the issue, then inspect the keyboard handling and labeling related to the SysRq/Print key. Compare the current behavior with the linked PRs #150 and #731. Done means the key is labeled SysRq and Alt+SysRq/Print can be followed by h without ending the combination.