Avoid direct constructors from JRuby

These classes either have been made abstract or will be made
abstract in the future. We should avoid using the direct
constructors from now on.

Author: headius

src/main/java/org/jruby/ext/openssl/StringHelper.java

@@ -63,7 +63,7 @@ static RubyString newString(final Ruby runtime, final byte[] bytes, final int co
     }
 
     static RubyString newString(final Ruby runtime, final CharSequence chars) {
-        return new RubyString(runtime, runtime.getString(), chars, ASCIIEncoding.INSTANCE);
+        return RubyString.newString(runtime, chars, ASCIIEncoding.INSTANCE);
     }
 
     static ByteList setByteListShared(final RubyString str) {
@@ -73,12 +73,12 @@ static ByteList setByteListShared(final RubyString str) {
 
     static RubyString newUTF8String(final Ruby runtime, final ByteList bytes) {
         ByteList byteList = new ByteList(RubyEncoding.encodeUTF8(bytes), UTF8Encoding.INSTANCE, false);
-        return new RubyString(runtime, runtime.getString(), byteList);
+        return RubyString.newString(runtime, byteList);
     }
 
     static RubyString newUTF8String(final Ruby runtime, final CharSequence chars) {
         ByteList byteList = new ByteList(RubyEncoding.encodeUTF8(chars), UTF8Encoding.INSTANCE, false);
-        return new RubyString(runtime, runtime.getString(), byteList);
+        return RubyString.newString(runtime, byteList);
     }
 
     static RubyString newStringFrozen(final Ruby runtime, final ByteList bytes) {