Pledge updates for FIP-0081

[BigLep]

Done Criteria

Pledge API is updated to account for FIP-0081

Why Important

User/Customer

Notes

1. go-state-type work is in implement the migration for FIP0081 go-state-types#313

[ZenGround0]

I would consider disposing of the ramping calculation and simply taking the max of PLEDGE_BEFORE_RAMP, PLEDGE_AFTER_RAMP. This way you can avoid any time dependent complexity. The difference in pledge should be small. And SPs can always withdraw any unused extra.