Validate terminal conditions of the merge block if no chain ancestor was valid in forkchoice

[g11tech]

Moving one of the tasks of

• Update forkchoice using latestValidHash updates from execution engine #4182
  as a separate issue, as the resolution isn't straight forward yet, and it not being addressed in Update forkchoice using latestValidHash updates from execution engine #4182 doesn't break backward compatibility as the EL is any way supposed to carry out validations on the terminal conditions of the chain its validating.

Raised in the R& D discord for discussions and how everyone else is addressing this. may be EL validations are just enough and we don't need to do anything apart from an exchange configuration matching.

lets say we optimistically synced past merge point, like (pre-merge), (syncing), (syncing).... for a long time, eventually with new finalized(s), and pruning of pre-merge block out of forkchoice
so now fcU chain is syncing,syncing,...syncing, now if the valid comein , the terminal conditions need to be verified of the terminal pow block,

(essentially each time one gets valid and tries to percolate and see that all ancestors in forkchoice of that chain are syncing which obviously will now be flipped to valid )

Question is how to get the handle of that terminal block to fetch its properties from the execution engine, it is quite possible that its on a sidechain of the terminal block which was fetched/cached by the merge block finder tracker

Although execution engine would have ran its own terminal validations before returning valid on that chain, so may be we can just happily accept it (which is what happens now as well), so do we need to run double check and how (and if we don't why do we need to run the check in the first place)
or should it be resolved via an exchange config call when this happens (and do validations there upon)

[g11tech]

since the mainnet has moved past the merge this issue is no more relevant as all weaksubjectivity checkpoints start post merge.