Merge bitcoin/bitcoin#28170: p2p: adaptive connections services flags

27f260aa6e net: remove now unused global 'g_initial_block_download_completed' (furszy)
aff7d92b15 test: add coverage for peerman adaptive connections service flags (furszy)
6ed53602ac net: peer manager, dynamically adjust desirable services flag (furszy)
9f36e591c5 net: move state dependent peer services flags (furszy)
f9ac96b8d6 net: decouple state independent service flags from desirable ones (furszy)
97df4e3887 net: store best block tip time inside PeerManager (furszy)

Pull request description:

  Derived from #28120 discussion.

  By relocating the peer desirable services flags into the peer manager, we
  allow the connections acceptance process to handle post-IBD potential
  stalling scenarios.

  The peer manager will be able to dynamically adjust the services flags
  based on the node's proximity to the tip (back and forth). Allowing the node
  to recover from the following post-IBD scenario:
  Suppose the node has successfully synced the chain, but later experienced
  dropped connections and remained inactive for a duration longer than the limited
  peers threshold (the timeframe within which limited peers can provide blocks). In
  such cases, upon reconnecting to the network, the node might only establish
  connections with limited peers, filling up all available outbound slots. Resulting
  in an inability to synchronize the chain (because limited peers will not provide
  blocks older than the `NODE_NETWORK_LIMITED_MIN_BLOCKS` threshold).

ACKs for top commit:
  achow101:
    ACK 27f260aa6e
  vasild:
    ACK 27f260aa6e
  naumenkogs:
    ACK 27f260aa6e
  mzumsande:
    Light Code Review ACK 27f260aa6e
  andrewtoth:
    ACK 27f260aa6e

Tree-SHA512: 07befb9bcd0b60a4e7c45e4429c02e7b6c66244f0910f4b2ad97c9b98258b6f46c914660a717b5ed4ef4814d0dbfae6e18e6559fe9bec7d0fbc2034109200953

src/net.h

@@ -1005,6 +1005,12 @@ public:
     /** Handle removal of a peer (clear state) */
     virtual void FinalizeNode(const CNode& node) = 0;
 
+    /**
+     * Callback to determine whether the given set of service flags are sufficient
+     * for a peer to be "relevant".
+     */
+    virtual bool HasAllDesirableServiceFlags(ServiceFlags services) const = 0;
+
     /**
     * Process protocol messages received from a given node
     *