fix: chainstore: store tipsetkeys in the blockstore

[arajasek]

Related Issues

filecoin-project/ref-fvm#1053

Proposed Changes

• Introduce a new PersistTipset method that replacs PersistBlockHeaders at all callsites (it's what we always want to do)
• Store the TSK in the PersistTipset method
• Drop unused AddBlock method

Additional Info

Checklist

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[Stebalien]

Not something we want to refactor now, but PutTipSet and PersistTipSet are confusing.

[Stebalien]

This may have performance implications (although it may also have been a premature optimization?).

[raulk]

Noting that we were already storing the tipset key here:

lotus/chain/store/store.go

Lines 653 to 663 in f438b1c

	tskBlk, err := ts.Key().ToStorageBlock()
	if err != nil {
	log.Errorf("failed to create a block from tsk: %s", ts.Key())
	return err
	}
	err = cs.chainLocalBlockstore.Put(ctx, tskBlk)
	if err != nil {
	log.Errorf("failed to put block for tsk: %s", ts.Key())
	return err
	}

Feel free to merge this as it looks strictly cleaner, but should probably remove the original write.