[BUG][typescript-fetch] query params ignores content application/json

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

the query parameter is not serialized as JSON, but exploded:

/customer/2000/audio/files/page?filters[durationMin]=151000&filters[durationMax]=337000

instead of:

/customer/2000/audio/files/page?filters=%7B%22durationMin%22%3A151000%2C%22durationMax%22%3A337000%7D

(obtained by encodeURIComponent(JSON.stringify({durationMin: 151000, durationMax: 337000})) )

openapi-generator version

6.0.1 but with locally installed, up-to-date typescript-fetch template

OpenAPI declaration file content or url

Full File as Gist

important lines:

        - in: query
          name: filters
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/QueryFilter"

Generation Details

openapi-generator generate -i ./openapi.yaml -g typescript-fetch -c ./swagger/clientgen.config.json -o ./src/lib/api/

./swagger/clientgen.config.json:

{
    "allowUnicodeIdentifiers": true,
    "modelPropertyNaming": "camelCase",
    "enumPropertyNaming": "camelCase",
    "paramNaming": "camelCase",
    "nullSafeAdditionalProps": true,
    "supportsES6": true,
    "typescriptThreePlus": true,
    "withoutRuntimeChecks": true,
    "legacyDiscriminatorBehavior": false
}

Steps to reproduce

1. generate with given config
2. call the api

Suggest a fix

this may be only a template issue. The function that currently creates the fetch params in the runtime
does not handle JSON serialization.

Start with modules/openapi-generator/src/main/resources/typescript-fetch/runtime.mustache, particularly the fetch-parameter logic around lines 114-157. Reproduce the issue using the linked OpenAPI declaration and the shown typescript-fetch generation command and configuration. Done means a query parameter declared with application/json is serialized as an encoded JSON value rather than exploded properties.