Enforce validators can only use the correct pubkey type

[ValarDragon]

The first commit on this branch mirrors #2714 before the commit chaos happened.

What remains to be done:

• Address anton's comment of separating validation and update logic (Enforce that validators use pubkey types from validator params #2714 (comment))
• Address review from Add ValidatorPubkeyTypes as a consensus param #2636

• Updated all relevant documentation in docs
• Updated all code comments where relevant
• Wrote tests
• Updated CHANGELOG_PENDING.md

[codecov-io]

Codecov Report

Merging #2739 into develop will increase coverage by <.01%.
The diff coverage is 79.16%.

@@             Coverage Diff             @@
##           develop    #2739      +/-   ##
===========================================
+ Coverage    62.68%   62.68%   +<.01%     
===========================================
  Files          212      212              
  Lines        17305    17327      +22     
===========================================
+ Hits         10847    10862      +15     
- Misses        5548     5552       +4     
- Partials       910      913       +3

Impacted Files	Coverage Δ
libs/common/string.go	81.08% <100%> (+4.41%)	⬆️
state/execution.go	74.89% <70.58%> (-1.42%)	⬇️
blockchain/pool.go	78.83% <0%> (-0.69%)	⬇️
consensus/reactor.go	65.76% <0%> (-0.12%)	⬇️
p2p/pex/pex_reactor.go	72.15% <0%> (+0.31%)	⬆️
p2p/pex/addrbook.go	69.39% <0%> (+0.48%)	⬆️

[ValarDragon]

I'm kind of confused about the pre-existing situation about how errors are handled in execution.go. If one validator update fails, won't all subsequent validator updates fail? Really we just want that one update to fail. I think that issue is distinct from this one (i.e. shouldn't block this PR), though I am still confused by it.

[melekes]

🍃 🌴 🌤

[ebuchman]

Oh damn, this needs to be updated - TxSize and BlockGossip were removed!

[melekes]

💎

[ebuchman]

Thanks Dev!