refactor: Replace string chain name constants with ChainTypes

This commit effectively moves the definition of these constants
out of the chainparamsbase to their own file.

Using the ChainType enums provides better type safety compared to
passing around strings.

The commit is part of an ongoing effort to decouple the libbitcoinkernel
library from the ArgsManager and other functionality that should not be
part of the kernel library.

src/kernel/chainparams.h

@@ -11,6 +11,7 @@
 #include <primitives/block.h>
 #include <protocol.h>
 #include <uint256.h>
+#include <util/chaintype.h>
 #include <util/hash_type.h>
 
 #include <cstdint>
@@ -114,8 +115,10 @@ public:
     uint64_t AssumedChainStateSize() const { return m_assumed_chain_state_size; }
     /** Whether it is possible to mine blocks on demand (no retargeting) */
     bool MineBlocksOnDemand() const { return consensus.fPowNoRetargeting; }
-    /** Return the network string */
-    std::string NetworkIDString() const { return strNetworkID; }
+    /** Return the chain type string */
+    std::string GetChainTypeString() const { return ChainTypeToString(m_chain_type); }
+    /** Return the chain type */
+    ChainType GetChainType() const { return m_chain_type; }
     /** Return the list of hostnames to look up for DNS seeds */
     const std::vector<std::string>& DNSSeeds() const { return vSeeds; }
     const std::vector<unsigned char>& Base58Prefix(Base58Type type) const { return base58Prefixes[type]; }
@@ -172,7 +175,7 @@ protected:
     std::vector<std::string> vSeeds;
     std::vector<unsigned char> base58Prefixes[MAX_BASE58_TYPES];
     std::string bech32_hrp;
-    std::string strNetworkID;
+    ChainType m_chain_type;
     CBlock genesis;
     std::vector<uint8_t> vFixedSeeds;
     bool fDefaultConsistencyChecks;