[Typescript] Generate oneOf schemas as type unions

[ksvirkou-hubspot]

Description of the PR

Generate type unions for schemas represented with oneOf format
as #2617 but for typescript generator
Sample input:

"inputFieldDependencies": {
   "type": "array",
   "items":{
      "oneOf":[
         {
            "$ref":"#/components/schemas/SingleFieldDependency"
         },
         {
            "$ref":"#/components/schemas/ConditionalSingleFieldDependency"
         }
      ]
   }
}

Sample output:

import { PublicConditionalSingleFieldDependency } from '../models/SingleFieldDependency';
import { PublicSingleFieldDependency } from '../models/ConditionalSingleFieldDependency';

export type PublicActionDefinitionInputFieldDependenciesInner = SingleFieldDependency | ConditionalSingleFieldDependency;

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:

  ./mvnw clean package 
  ./bin/generate-samples.sh ./bin/configs/*.yaml
  ./bin/utils/export_docs_generators.sh
  

• File the PR against the correct branch: master (upcoming 7.6.0 minor release - breaking changes with fallbacks), 8.0.x (breaking changes without fallbacks)
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

Related issues:

#9305

[ksvirkou-hubspot]

@TiFu @taxpon @sebastianhaas @kenisteward @Vrolijkx @macjohnny @topce @akehir @petejohansonxo @amakhrov @davidgamero @mkusaka