Merge #11389: Support having SegWit always active in regtest (sipa, ajtowns, jnewbery)

d61845818 Have SegWit active by default (Pieter Wuille)
4bd89210a Unit tests for always-active versionbits. (Anthony Towns)
d07ee77ab Always-active versionbits support (Pieter Wuille)
18e071841 [consensus] Pin P2SH activation to block 173805 on mainnet (John Newbery)
526023aa7 Improve handling of BIP9Deployment limits (Anthony Towns)

Pull request description:

  Most tests shouldn't have to deal with the now-historical SegWit activation transition (and other deployments, but SegWit is certainly the hardest one to accomodate).

  This PR makes a versionbits starttime of -1 equal to "always active", and enables it by default for SegWit on regtest. Individual tests can override this by using the existing `-vbparams` option.

  A few unit tests and functional tests are adapted to indeed override vbparams, as they specifically test the transition.

  This is in preparation for wallet SegWit support, but I thought having earlier eyes on it would be useful.

Tree-SHA512: 3f07a7b41cf46476e6c7a5c43244e68c9f41d223482cedaa4c02a3a7b7cd0e90cbd06b84a1f3704620559636a2268f5767d4c52d09c1b354945737046f618fe5

src/test/test_bitcoin.cpp

@@ -118,6 +118,9 @@ TestingSetup::~TestingSetup()
 
 TestChain100Setup::TestChain100Setup() : TestingSetup(CBaseChainParams::REGTEST)
 {
+    // CreateAndProcessBlock() does not support building SegWit blocks, so don't activate in these tests.
+    // TODO: fix the code to support SegWit blocks.
+    UpdateVersionBitsParameters(Consensus::DEPLOYMENT_SEGWIT, 0, Consensus::BIP9Deployment::NO_TIMEOUT);
     // Generate a 100-block chain:
     coinbaseKey.MakeNewKey(true);
     CScript scriptPubKey = CScript() <<  ToByteVector(coinbaseKey.GetPubKey()) << OP_CHECKSIG;