[typescript*] drop support typescript below 4.0

Created by: mkusaka

Changed the lower limit of typescript version generated by the typescirpt-related generator to 4.0 as well as https://github.com/OpenAPITools/openapi-generator/pull/12102

See https://github.com/OpenAPITools/openapi-generator/pull/12102 for motivation and benefits.

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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) and @wing328

closed

added Client: TypeScript label

changed milestone to %6.0.0

added Decommission label

added Breaking change (without fallback) label

mentioned in merge request !11689 (merged)

mentioned in issue #10684 (closed)