Support Helidon Path Variable Patterns

[SentryMan]

Now can do:

@Path("test")
@Controller
public class TestController {

  @Get("/peppermint/{patty:\\d+}")
  String pattern(String patty) {
    return patty;
  }

  @Get("/minus/{+plus}")
  String patternPlus(String plus) {
    return plus;
  }
}

and the controller will generate like

@Generated("avaje-helidon-generator")
@Component
public class TestController$Route implements HttpFeature {

  private final TestController controller;
  private final JsonType<String> stringJsonType;

  public TestController$Route(TestController controller, Jsonb jsonb) {
    this.controller = controller;
    this.stringJsonType = jsonb.type(String.class);
  }

  @Override
  public void setup(HttpRouting.Builder routing) {
    routing.get("/test/peppermint/{patty:\\d+}", this::_pattern);
    routing.get("/test/minus/{+plus}", this::_patternPlus);
  }

  private void _pattern(ServerRequest req, ServerResponse res) throws Exception {
    res.status(OK_200);
    var pathParams = req.path().pathParameters();
    var patty = pathParams.first("patty").get();
    var result = controller.pattern(patty);
    if (result == null) {
      res.status(NO_CONTENT_204).send();
    } else {
      res.headers().contentType(MediaTypes.APPLICATION_JSON);
      res.send(result);
    }
  }

  private void _patternPlus(ServerRequest req, ServerResponse res) throws Exception {
    res.status(OK_200);
    var pathParams = req.path().pathParameters();
    var plus = pathParams.first("plus").get();
    var result = controller.patternPlus(plus);
    if (result == null) {
      res.status(NO_CONTENT_204).send();
    } else {
      res.headers().contentType(MediaTypes.APPLICATION_JSON);
      res.send(result);
    }
  }
}

Fixes #386