Change get_latest_attesting_balance() to get_weight()

[benjaminion]

Proposal to rename get_latest_attesting_balance() in the fork choice to get_weight().

I am trying to write about this function, and it's frustratingly difficult since the name "latest attesting balance" is quite ambiguous.

A few reasons:

• "Weight" better reflects this quantity's role in the protocol. It chimes with the "heaviest" in GHOST.
• Validators attest to a block directly, and only implicitly to its ancestors. This is the origin of the ambiguity - I want to distinguish between the direct latest attesting balance of a block (those validators who attested to that block), and the latest attesting balance in the sense of this function, which is the sum of all those direct latest attesting balances for all its descendants. It's all quite cumbersome. Calling the latter the block's weight would be much simpler.
• Now that we have included proposer boost in the calculation, "latest attesting balance" is not really accurate any more.

[djrtwo]

Right, I see the what-could-be-annoying ambiguity this name brings to explaining to outsiders/new spec readers. I'm not opposed to making this shift

[hwwhww]

It makes sense to me. 👍

I git-blame it, this function was about "getting the latest attesting balance" at the beginning but then changed a lot after iterations.

get_weight sounds good to me. Another idea is get_score as we the return value is attestation_score + proposer_score. Either way is better than status-quo.

It would be great to get more 👍 from client teams before merging this phase0 change.

[djrtwo]

CC: @adiasg who spends a lot of time on fc specs