fix: drop reflective access warnings to java.time.* classes

[mjg123]

Java module system gives warnings on reflective access to java.time.* private fields, which are performed by Jackson when using TwilioRestClient.

Jackson provides a JavaTimeModule which configures an ObjectMapper to use public methods instead of reflective accesss to private fields in classes in java.time.

This PR adds the dependency for JavaTimeModule and adds it to the ObjectMapper created by TwilioRestClient, which removes all the warnings that I have seen.

Fixes #597

A short description of what this PR does.

Checklist

• [x] I acknowledge that all my contributions will be made under the project's license
• [x] I have made a material change to the repo (functionality, testing, spelling, grammar)
• [x] I have read the Contribution Guidelines and my PR follows them
• [x] I have titled the PR appropriately
• [x] I have updated my branch with the main branch
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have added necessary documentation about the functionality in the appropriate .md file
• [ ] I have added inline documentation to the code I modified

If you have questions, please file a support ticket, or create a GitHub Issue in this repository.

[mjg123]

A note on testing:

Considering this code

package com.twilio.helperv8;

import com.twilio.Twilio;
import com.twilio.rest.api.v2010.account.Message;
import com.twilio.type.PhoneNumber;

public class Helper8Warning {

    public static void main(String[] args) {
        Twilio.init(
            System.getenv("TWILIO_ACCOUNT_SID"),
            System.getenv("TWILIO_AUTH_TOKEN"));

        Message.creator(
            new PhoneNumber("<My phone number>"),
            new PhoneNumber("<My Twilio number>"),
            "Warning!"
        ).create();
    }
}

Without this patch - SMS is sent, 5 lines of warnings are sent to stderr:

WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by com.fasterxml.jackson.databind.util.ClassUtil (file:/home/mjg/.m2/repository/com/fasterxml/jackson/core/jackson-databind/2.11.3/jackson-databind-2.11.3.jar) to field java.time.ZonedDateTime.offset
WARNING: Please consider reporting this to the maintainers of com.fasterxml.jackson.databind.util.ClassUtil
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release

With this patch - SMS is sent, no warnings generated.

So I'm not sure how a unit test could be written for this.

[mjg123]

Also raised as https://github.com/twilio/twilio-java/issues/597