Avoid SuppressWarnings of "this-escape" in Java Setting hierarchy

@andsel is already working on this.

Since Oct 11, 2024.

• #16543 by @andsel — open

With #16496 and commit 5ca068693a6cbec28bf794cb1cf6f560c5053351 in #16490 were introduced some `@SupressWarning` annotations to avoid errors with JDK 21 like:

```
/buildkite/builds/bk-agent-prod-k8s-1728654414425952824/elastic/logstash-pull-request-pipeline/logstash-core/src/main/java/org/logstash/settings/BaseSetting.java:105: warning: [this-escape] possible 'this' escape before subclass is fully initialized
--
  | validate(defaultValue);
  | ^pileJava
  | error: warnings found and -Werror specified
  | 1 error
  | 1 warning
  |  
  | > Task :logstash-core:compileJava FAILED
  |  
  | FAILURE: Build failed with an exception.

```

As per comment https://github.com/elastic/logstash/pull/16490#pullrequestreview-2360999039 this issue is to ask for removal of such annotations and leverage static method instead of calling instance methods on non-completely initialised instances.

Start with logstash-core/src/main/java/org/logstash/settings/BaseSetting.java and inspect the warning location around validate(defaultValue). Review the suppress-warning annotations introduced by #16496 and commit 5ca068693a6cbec28bf794cb1cf6f560c5053351, along with linked PR #16543. Done means removing the relevant annotations and avoiding instance-method calls during incomplete initialization by using static methods where appropriate.

Written by the indexing model from the issue text.