[JAVA] Remove [this-escape] warnings in generated ApiClient classes

[welandaz]

This PR is basically a follow-up to an earlier one where some of these issues have been addressed, but not completely.

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[welandaz]

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)

[welandaz]

The usage of getDefaultBaseUri() in the constructor is fine until the user overrides it and references any dynamically calculated value from a field/method (static string would be fine).

A proper fix would be to have a constructor that accepts a basePath and doesn't offer a default value (or leave this method as is, but remove it from the constructor and introduce a factory method that creates the ApiClient and invokes updateBaseUri right after). That would be a breaking change, though it would address the problem.

This change is a compromise of sorts, where a default value is taken directly from the variable (which user can still override or call updateBaseUri later). The getter is simply a getter now and isn't invoked anywhere.

[wing328]

A proper fix would be to have a constructor that accepts a basePath

agreed. that's what the okhttp-gson client offers.

https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/resources/Java/libraries/okhttp-gson/ApiClient.mustache#L211

and we can leave it to another PR instead