Change features default behavior in Env (RIPD-1460):

Enable all supported amendments in Env by default. Rename `features()`
to `with_features()` and add `all_features_except()` to support feature
subsets in Env. Refactor internal feature handling based on a bitset.

src/test/app/Regression_test.cpp

@@ -171,7 +171,7 @@ struct Regression_test : public beast::unit_test::suite
                     .set("minimum_txn_in_ledger_standalone", "3");
                 return cfg;
             }),
-            features(featureFeeEscalation));
+            with_features(featureFeeEscalation));
         Env_ss envs(env);
 
         auto const alice = Account("alice");