Fixed serialization of date-time query parameters.

[Reinhard-PTV]

Fixed date-time query parameter handling for java native java8 and typescript-fetch.

#8615

@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)
@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) @nmuesch (2021/01)

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[TiFu]

Thank you for the PR! TypeScript changes LGTM

[wing328]

CiricleCI tests passed via https://app.circleci.com/pipelines/github/OpenAPITools/openapi-generator/8708/workflows/3afa36ae-0b8e-4de3-81dc-0c9dcc6b8368/jobs/22286

[wing328]

@Reinhard-PTV thanks for the PR, which has been included in the v5.1.0 release: https://twitter.com/oas_generator/status/1373636654024380423