[Java][apache-httpclient] Use EntityUtils#toString instead of Scanner for deserialization

[AB-xdev]

Fixes #16818

EntityUtils#toString automatically selects the correct encoding based on the received request.
Scanner currently uses the JVM default encoding, which doesn't always work.

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package 
  ./bin/generate-samples.sh ./bin/configs/*.yaml
  ./bin/utils/export_docs_generators.sh
  

  (For Windows users, please run the script in Git BASH)
  Commit all changed files.
  This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
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Further notes

• When building on Windows many files are generated with \ instead of / (had to revert the changes manually) - This is behavior is already present on the current master branch

[wing328]

please update the samples so that the CI can verify the change: https://github.com/OpenAPITools/openapi-generator/actions/runs/8095529271/job/22155733266?pr=17998

[AB-xdev]

Oh, I overlooked this...
Anyway I updated it accordingly, now it should work :)

[wing328]

lgtm. thanks for the fix.