Deperected api

[Ao-senXiong]

Merge after #96

[sohah]

@Ao-senXiong , thank you for your contributions. I have a few comments on this pull request:

1. I see warnings from deprecated Gradle API. I think you can safely remove jcenter(). I also can see a reference to JavaPluginConvention which is also producing a couple of warnings. Can you investigate where this is being used?
2. for SymbolicStringBuilder, can you please explain why you need java.lang.ref.Cleaner for Java 11 support?

[Ao-senXiong]

1, I think we need to investigate on gradle 9.0 deprecation in another PR. This PR is more on Java API deprecation. For your question 2 for SymbolicStringBuilder, can you please explain why you need java.lang.ref.Cleaner for Java 11 support?, because _finalize method is deprecated since Java 9. So it is need to use the cleanner.

[sohah]

@Ao-senXiong

1. it would be nice to fix these gradle warning if possible, you have already done some of that, right?
2. the usage of cleaner needs some fixes. I think you should capture the Cleanable from the register method, then invoke cleanable.clean() in the place where the _finalize() is right now. That way you've actually invoked the cleaning whenever the _finalize is invoked