fix: refine VT switch

[calsys456]

1. Add callback for disableRender, make sure logics are execute in correct order;
2. Activate treeland session before acknowledge VT switch, to ensure all GUI elements are under a prepared state before next possible VT switch issued by keyboard;
3. Make event functions static;
4. Add comments, make code more readable;

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[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: apr3vau, zccrs

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