spec 1.1.6 - Applying proposer boost to fork-choice

[g11tech]

Motivation
In order to prevent some attack scenarios, timely receipt of the block needs to be rewarded with proper boost as per CL spec 1.1.6 (the calculation of which was fixed in spec 1.1.7)

This PR implements following CL spec 1.1.6 changes along with spec 1.1.7 calc fixes

• proposer boost
• enables the proposer boost checks in fork-choice spec tests version 1.1.8
• putting the proposer boost behind the flag --chain.proposerBoostEnabled

Closes #3506, #3438,
Partially closes #3483

[codeclimate]

Code Climate has analyzed commit 067debc and detected 1 issue on this pull request.

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Category	Count
Complexity	1

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[codecov]

Codecov Report

Merging #3540 (553aeaa) into master (1bd730a) will decrease coverage by 0.23%.
The diff coverage is n/a.

❗ Current head 553aeaa differs from pull request most recent head 067debc. Consider uploading reports for the commit 067debc to get more accurate results

@@            Coverage Diff             @@
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- Coverage   37.40%   37.16%   -0.24%     
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  Files         311      321      +10     
  Lines        8374     8696     +322     
  Branches     1299     1348      +49     
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+ Hits         3132     3232     +100     
- Misses       5093     5319     +226     
+ Partials      149      145       -4     

[g11tech]

since lighthouse's proposer score computation is still pretty cheap, reverted to that approach in order to keep the forkChoice closer to lighthouse's implementation.

✓ computeProposerBoostScoreFromBalances                               6907.508 ops/s    144.7700 us/op        -     206061 runs   30.0 s

[twoeths]

this function should be called once per justified balances at most, we can even precompute it in getEffectiveBalances() to avoid an extra for loop over justified balances, and send both proposerBoostScore and justifiedBalances to forkchoice over onBlock()

[g11tech]

yes, good idea 👍

[g11tech]

actually it could require a bit more bookeeping as there is one place where justified is updated with the bestJustifiedBalances, so will also have to track bestProposerBoostScore

[g11tech]

@tuyennhv now score is calculated atmost once per justified balances

[dapplion]

Excellent! Looks great 🔥 🔥 I've committed on top to make the feature flag visible