[JAVA] Address [rawtypes] and [this-escape] warnings in generated API clients

[welandaz]

This work resolves the following issue - #18384

Integration tests have been executed manually according to the contribution guidelines.

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[wing328]

thanks for the PR

cc @bbdouglas (2017/07) @sreeshas (2017/08) @jfiala (2017/08) @lukoyanov (2017/09) @cbornet (2017/09) @jeff9finger (2018/01) @karismann (2019/03) @Zomzog (2019/04) @lwlee2608 (2019/10) @martin-mfg (2023/08)

[wing328]

generally i'm ok with the PR but if later users have a use case that need protected method here for example, we will need to provide a way to fallback.