Mechanism to reduce the need for two network upgrades for F3 activation to one

[BigLep]

Done Criteria

An community-agreed mechanism exists within Filecoin implementations (Lotus, Forest, Venus) that enables F3 to be activated with only one more network upgrade (nv25) rather than two.

Why Important

See #800

Notes

1. See more details and the rationale in Design a mechanism to reduce the need for two network upgrades for F3 activation to one #800
2. This is serving as an overarching tracking issue for this effort (rather than having the design issue be the parent).