[BUG][typescript][regression] Invalid path separator for imports on Windows

Created by: adamstoffel

Description

Typescript clients generated on Windows have invalid import paths due to the wrong path separator being used.

Expected Code

import { Pet } from '../models/Pet';

Actual Code

import { Pet } from '..\models\Pet';

openapi-generator version

Any version >= 6.1.0

OpenAPI declaration file content or url

https://raw.githubusercontent.com/openapitools/openapi-generator/master/modules/openapi-generator/src/test/resources/2_0/petstore.yaml

Command line used for generation

java -jar modules\openapi-generator-cli\target\openapi-generator-cli.jar generate -i https://raw.githubusercontent.com/openapitools/openapi-generator/master/modules/openapi-generator/src/test/resources/2_0/petstore.yaml -g typescript -o c:\temp\typescript_client

Steps to reproduce

Just generate source code for typescript.

Related issues/PRs

This was previously fixed (issue #7174 (closed), pull #7175) but regressed in pull #12957.

Suggest a fix/enhancement

Use / instead of File.Separator. File.Separator is \ in Windows, which is invalid Typescript.

Method to fix is toModelImport in modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/TypeScriptClientCodegen.java:

Current code:

    public String toModelImport(String name) {
        return ".." + File.separator + modelPackage() + File.separator + toModelName(name);
    }

Corrected code:

    public String toModelImport(String name) {
        // Use `/` instead of `File.Separator`. `File.Separator` is `\` in Windows, which is invalid Typescript.
        return "../" modelPackage() + "/" + toModelName(name);
    }