Fix java rest client ApiClient template to properly assign ObjectMapper

[CaptainAye]

Description:
The changes fix the ApiClient mustache template for java RestClient generator. Some of the constructors didn't properly pass the ObjectMapper parameter on, leading to creating default mapper even if the consumer passed custom instance.
Additionally, PR refactors the ApiClient constructors in order to move the creation logic to the one, most specific, constructor.

The pr fixes #19667

Technical committee Java:
@martin-mfg, @lwlee2608, @Zomzog, @karismann, @jeff9finger, @cbornet, @lukoyanov, @jfiala, @sreeshas, @bbdouglas

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[wing328]

thanks for the PR

please follow step 3 to update the samples so that the CI can test the change properly

[CaptainAye]

thanks for the PR

please follow step 3 to update the samples so that the CI can test the change properly

I added all the generated changes to the pr.

[wing328]

thanks again for the PR

did you test the fix locally to confirm it addresses the issue mentioned in the PR?

[CaptainAye]

thanks again for the PR

did you test the fix locally to confirm it addresses the issue mentioned in the PR?

Yes, I verified that the ObjectMapper is being properly passed to the ApiClient from any constructor, which was not the case previously.
I am happy to add some unit tests as well if it's required.