Add ChainstateManager::m_adjusted_time_callback

This decouples validation.cpp from netaddress.cpp (transitively,
timedata.cpp, and asmap.cpp).

This is important for libbitcoinkernel as:

- There is no reason for the consensus engine to be coupled with
  netaddress, timedata, and asmap
- Users of libbitcoinkernel can now easily supply their own
  std::function that provides the adjusted time.

See the src/Makefile.am changes for some satisfying removals.

src/rpc/mining.cpp

@@ -27,6 +27,7 @@
 #include <script/script.h>
 #include <script/signingprovider.h>
 #include <shutdown.h>
+#include <timedata.h>
 #include <txmempool.h>
 #include <univalue.h>
 #include <util/strencodings.h>
@@ -371,7 +372,7 @@ static RPCHelpMan generateblock()
         LOCK(cs_main);
 
         BlockValidationState state;
-        if (!TestBlockValidity(state, chainman.GetParams(), chainman.ActiveChainstate(), block, chainman.m_blockman.LookupBlockIndex(block.hashPrevBlock), false, false)) {
+        if (!TestBlockValidity(state, chainman.GetParams(), chainman.ActiveChainstate(), block, chainman.m_blockman.LookupBlockIndex(block.hashPrevBlock), GetAdjustedTime, false, false)) {
             throw JSONRPCError(RPC_VERIFY_ERROR, strprintf("TestBlockValidity failed: %s", state.ToString()));
         }
     }
@@ -640,7 +641,7 @@ static RPCHelpMan getblocktemplate()
             if (block.hashPrevBlock != pindexPrev->GetBlockHash())
                 return "inconclusive-not-best-prevblk";
             BlockValidationState state;
-            TestBlockValidity(state, chainman.GetParams(), active_chainstate, block, pindexPrev, false, true);
+            TestBlockValidity(state, chainman.GetParams(), active_chainstate, block, pindexPrev, GetAdjustedTime, false, true);
             return BIP22ValidationResult(state);
         }