Decouple RegTestChainParams from ArgsManager

RegTest chain params can now be initialized by configuring a
RegTestOptions struct, or with ArgsManager. This offers an interface for
creating RegTestChainParams without a gArgs object.

src/deploymentinfo.h

@@ -7,6 +7,7 @@
 
 #include <consensus/params.h>
 
+#include <optional>
 #include <string>
 
 struct VBDeploymentInfo {
@@ -26,4 +27,6 @@ inline std::string DeploymentName(Consensus::DeploymentPos pos)
     return VersionBitsDeploymentInfo[pos].name;
 }
 
+std::optional<Consensus::BuriedDeployment> GetBuriedDeployment(const std::string_view deployment_name);
+
 #endif // BITCOIN_DEPLOYMENTINFO_H