[compatibilty] Fnlock & Winlock

[hdhoang]

The stock firmware has the following locking functions:

• Fn + LMeta: Winlock
• Alt + Alt: Fnlock

These were often confusing and then removed in the 1.40.02 beta fw. But people who are using these features wouldn't complain on reddit or update to 1.40.02. We should support that use case somehow.

I think the Winlock implementation could be a mostly-transparent layer, where KeyIndex::LMeta is mapped to No action instead.

Fnlock could be LayerOn/Off/Toggle(FN).

I also remember a comment on reddit that Fn + Alt is Altlock(?), where someone replied "learn something new everyday". Can anyone confirm?