Add test modules and corresponding unit tests

[linghengqian]

What kind of change does this PR introduce? (check at least one)

• [ ] Bugfix
• [x] Feature
• [ ] Code style
• [x] Refactor
• [ ] Doc
• [x] Other, please describe:

The description of the PR:

• For https://github.com/baomidou/dynamic-datasource-spring-boot-starter/issues/475 .
• Add test modules and corresponding unit tests.
• The core code is put into the core module.
• I plan to add two separate test modules for javax ee and jakarta ee namespaces, I first initialized part of tests for javax ee namespace.
• The base Github Actions CI includes a package task for the core and a test task for the test module.
• For other database tests, I hope to complete it through testcontainers in other PRs. First complete the testing of h2database 2.x.
• Since setup-java no longer contains the initial jdk7 image, use jdk8 as the core build test image.
• test-ci I recommend testing only jdk17 and jdk19, as this will simplify what we need to test, especially to exclude the use of lombok.

Other information:

[linghengqian]

• Not sure why CodeQL keeps failing. My local normal.

[linghengqian]

@huayanYu Let me know your review.