[BUG] [TypeScript] Generated TypeScript dependency version conflict when generated module nested in another project

Created by: karlvr

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• [HEAD] What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Bounty to sponsor the fix (example)

Description

TypeScript looks in parent folders for node_modules/@types folders from which to load type definitions. If you nest the openapi generated TypeScript module in subfolder of a folder containing a node_modules which depends upon a later version of TypeScript, then when building the generated module, TypeScript finds the other node_modules/@types, tries to load them and fails.

openapi-generator version

HEAD (4.0.0). It is not a regression.

Steps to reproduce

npm init -y
npm install -D @types/jest
mkdir gen
openapi-generator generate -i http://petstore.swagger.io/v2/swagger.json -g typescript-fetch -o gen
cd gen
tsc

The tsc command fails due to the types that it doesn't understand.

Related issues/PRs

I am about to push a PR.