versionbits: Expose StateName function

Rather than essentially duplicating StateName in the unit tests, expose
it via the impl header.

src/test/versionbits_tests.cpp

@@ -16,18 +16,6 @@
 /* Define a virtual block time, one block per 10 minutes after Nov 14 2014, 0:55:36am */
 static int32_t TestTime(int nHeight) { return 1415926536 + 600 * nHeight; }
 
-static std::string StateName(ThresholdState state)
-{
-    switch (state) {
-    case ThresholdState::DEFINED:   return "DEFINED";
-    case ThresholdState::STARTED:   return "STARTED";
-    case ThresholdState::LOCKED_IN: return "LOCKED_IN";
-    case ThresholdState::ACTIVE:    return "ACTIVE";
-    case ThresholdState::FAILED:    return "FAILED";
-    } // no default case, so the compiler can warn about missing cases
-    return "";
-}
-
 class TestConditionChecker : public AbstractThresholdConditionChecker
 {
 private:

src/versionbits.cpp

@@ -302,7 +302,7 @@ std::vector<std::pair<int, bool>> VersionBitsCache::CheckUnknownActivations(cons
     return result;
 }
 
-static std::string StateName(ThresholdState state)
+std::string StateName(ThresholdState state)
 {
     switch (state) {
     case ThresholdState::DEFINED: return "defined";

src/versionbits_impl.h

@@ -25,6 +25,9 @@ enum class ThresholdState : uint8_t {
     FAILED,    // For all blocks once the first retarget period after the timeout time is hit, if LOCKED_IN wasn't already reached (final state)
 };
 
+/** Get a string with the state name */
+std::string StateName(ThresholdState state);
+
 /**
  * Abstract class that implements BIP9-style threshold logic, and caches results.
  */