[REQ] Ability to configure target javascript version for typescript compiler in typescript generators

Is your feature request related to a problem? Please describe.

When porting the typescript-angular client generator to angular 13, I wanted to update the versions in the the generated tsconfig.json.
The file is currently hardcoded to es6 or es5 depending on a 'supportES6' common to all typescript clients.

It is used to generate the tsconfig. The following snippet has been copy/pasted to most generator templates:

 "target": "{{#supportsES6}}es6{{/supportsES6}}{{^supportsES6}}es5{{/supportsES6}}",
 "module": "{{#supportsES6}}es6{{/supportsES6}}{{^supportsES6}}commonjs{{/supportsES6}}",
{{^supportsES6}}
    "lib": [
      "es6",
      "dom"
    ],
    {{/supportsES6}}

And in some template, a corejs dependency is added for non-es6 targets.

Concerning the target javascript platform:

• Each generators may support a subset of javascript target platforms
• An end-user may want to specify a target platform, and take care of providing polyfills

Concerning the module configuration:

• An end user may want to overrides the gerenated module format depending on how the module is impored

Concerning the addition of a core-js dependency:

• This is polyfill library, to provide runtime librairies to the javascript platform, and should not be required for typescript compilation.
• It is not imported in the generated typescript-aurelia sample client, so the dependency sees unneeded.

Concerning the lib to include in typescript compilation:

• This should be derived from the target platform. eg when targeting es2017 libs up to es2017 should be provided to the compiler.
• By default, typescript includes the librairies of the target specified, so this option could probably be ignored.

Describe the solution you'd like

A more future-proof way to configure and handle javascript targets.

Im not sure Ive considered all options so this issue is more to sparkle discussion and query a consensus.

In my opinion we should be left with

• each generator defaulting a target and module` in their tsconfig.json
• no generator specifying additional lib unless required
• one tsModule option for the enduser to override
• one tsTarget option for the enduser to override.

Describe alternatives you've considered

Adding a supportsES2020 config flag

Additional context

https://github.com/OpenAPITools/openapi-generator/pull/10877

Start by reviewing the TypeScript generator templates and the linked pull request #10877, focusing on how generated tsconfig.json files use supportsES6, target, module, lib, and core-js. Done means reaching consensus on the configuration options and defaults, then applying and validating that approach across the affected TypeScript generators.