This notably fixes:

• JSON query param serialization
• array serialization with style=form and explode = true

The first commits of the patch introduces integration tests for query
parameters serialization in
samples/client/others/typescript-angular-v20:

• samples/client/others/typescript-angular-v20/projects/app/src/api.query_param_deep_object.spec.ts (move of an existing test)
• samples/client/others/typescript-angular-v20/projects/app/src/api.query_param_form.spec.ts (new test)
• samples/client/others/typescript-angular-v20/projects/app/src/api.query_param_json.spec.ts (new test)

They should be executed as part of CircleCI.
The last commit fixes the issue.
Fixes are in the following files:

• modules/openapi-generator/src/main/resources/typescript-angular/api.base.service.mustache
• modules/openapi-generator/src/main/resources/typescript-angular/api.service.mustache
• modules/openapi-generator/src/main/resources/typescript-angular/encoder.mustache

As the class HttpParams from Angular is specially designed for the
mimetype: application/x-www-form-urlencoded it does not support
the range of query parameters defined by the OpenAPI specification.
To workaround this issue, this patch introduces a custom
OpenAPIHttpParams class which supports a wider range of query param
styles.

Note that as HttpClient is used afterwards, the class
OpenApiHttpParams has a method to convert it into a HttpParams from
Angular with a no-op HttpParameterCodec to avoid double serialization of
the query parameters.

Fixes #21934 and #20998.

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:

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  (For Windows users, please run the script in WSL)
  Commit all changed files.
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• File the PR against the correct branch: master (upcoming 7.x.0 minor release - breaking changes with fallbacks), 8.0.x (breaking changes without fallbacks)
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  @TiFu (2017/07) @taxpon (2017/07) @sebastianhaas (2017/07) @kenisteward (2017/07) @Vrolijkx (2017/09) @macjohnny (2018/01) @topce (2018/10) @akehir (2019/07) @petejohansonxo (2019/11) @amakhrov (2020/02) @davidgamero (2022/03) @mkusaka (2022/04) @joscha (2024/10)