Spring Migrate to TestNG Engine for the JUnit Platform

To simplify our Gradle build in the spring-test module, we should investigate migrating to the TestNG Engine for the JUnit Platform and consolidate all tests into a single Gradle test task.

Comment From: sbrannen

Currently blocked due to https://github.com/junit-team/testng-engine/issues/13

Comment From: sbrannen

Closed via 0b552a3534e080ca842c7f08a9950233ce56e72e and e29867b96e835a53d0222ad666273b5e93c800a6.