test: refactor: Accept any RandomNumberGenerator in RandMoney

Accepting any Rng in RandMoney makes tests more flexible to use a
different Rng. Also, passing in the Rng clarifies the call sites, so
that they all use g_rand_ctx explicitly and consistently.

src/test/coins_tests.cpp

@@ -182,7 +182,7 @@ void SimulationTest(CCoinsView* base, bool fake_best_block)
 
             if (InsecureRandRange(5) == 0 || coin.IsSpent()) {
                 Coin newcoin;
-                newcoin.out.nValue = InsecureRandMoneyAmount();
+                newcoin.out.nValue = RandMoney(m_rng);
                 newcoin.nHeight = 1;
 
                 // Infrequently test adding unspendable coins.