feat(developer): infer key id automatically from key cap in touch layout editor

When a new longpress key is added to the keyboard, a T_new_xxx label is created for the key. At the moment of creation, Developer doesn’t know what character(s) or other actions will be assigned to the key, nor whether additional logic will be needed in the .kmn file, so it can’t really know what U_xxxx label might be needed.

Perhaps there could be an option for keys on the touch layout that would change the label to match the content.

From: https://community.software.sil.org/t/longpress-touch-confusion/7113/8 @DavidLRowe