Merge #16443: refactor: have CCoins* data managed under CChainState

582d2cd747 Cover UTXO set access with lock annotations (James O'Beirne)
5693530685 refactor: have CCoins* data managed under CChainState (James O'Beirne)
fae6ab6aed refactor: pcoinsTip -> CChainState::CoinsTip() (James O'Beirne)

Pull request description:

  This is part of the [assumeutxo project](https://github.com/bitcoin/bitcoin/projects/11):

  Parent PR: #15606
  Issue: #15605
  Specification: https://github.com/jamesob/assumeutxo-docs/tree/2019-04-proposal/proposal

  ---

  This change encapsulates UTXO set data within CChainState instances, removing global data `pcoinsTip` and `pcoinsviewdb`. This is necessary if we want to maintain multiple chainstates with their own rendering of the UTXO set.

  We introduce a class CoinsViews which consolidates the construction of a CCoins* hierarchy.

  This commit could be broken into smaller pieces, but it would require more ephemeral diffs to, e.g., temporarily change CCoinsViewDB's constructor invocations.

ACKs for top commit:
  Sjors:
    reACK 582d2cd747
  MarcoFalke:
    ACK 582d2cd747

Tree-SHA512: ec9d904fe5dca8cd2dc4b7916daa5d8bab30856dd4645987300f905e0a19f9919fce4f9d1ff03eda982943ca73e6e9a746be6cf53b46510de36e8c81a1eafba1

src/interfaces/node.cpp

@@ -232,7 +232,7 @@ public:
     bool getUnspentOutput(const COutPoint& output, Coin& coin) override
     {
         LOCK(::cs_main);
-        return ::pcoinsTip->GetCoin(output, coin);
+        return ::ChainstateActive().CoinsTip().GetCoin(output, coin);
     }
     std::string getWalletDir() override
     {