[BUG][typescript-fetch] any-typed multipart form parameter emits unqualified anyToJSON (does not compile)

[donald]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

A multipart/form-data parameter that has no type at all ("any type") makes typescript-fetch
emit a call to a bare anyToJSON(...). The generated apis/*.ts only imports the runtime as
* as runtime, so that identifier does not exist and the generated code does not compile.

The free-form-object case is already handled — runtime.anyToJSON — but the any-type case falls through
to {{dataType}}ToJSON, and for an any-typed parameter dataType is any, so it renders as anyToJSON.

openapi-generator version

7.25.0-SNAPSHOT, built from master at commit 4aed9c1c635.

OpenAPI declaration file content or url

openapi: 3.0.3
info: { title: t, version: 1.0.0 }
paths:
  /upload:
    post:
      operationId: upload
      requestBody:
        content:
          multipart/form-data:
            schema:
              type: object
              properties:
                file: { type: string, format: binary }
                meta: { description: can be any type }   # no type -> "any type"
      responses: { "200": { description: ok } }

Generation Details

java -jar modules/openapi-generator-cli/target/openapi-generator-cli.jar generate \
  -i spec.yaml -g typescript-fetch -o out

Steps to reproduce

1. Save the spec above as spec.yaml
2. Run the command above
3. Look at out/apis/DefaultApi.ts

Actual output

import * as runtime from '../runtime';
...
formParams.append('meta', new Blob([JSON.stringify(anyToJSON(requestParameters['meta']))], { type: "application/json", }));
//                                                 ^^^^^^^^^ not imported, not defined

tsc fails with TS2304: Cannot find name 'anyToJSON'.

Expected output

formParams.append('meta', new Blob([JSON.stringify(runtime.anyToJSON(requestParameters['meta']))], { type: "application/json", }));

anyToJSON is exported by runtime.ts (added in #1877) and is already referenced correctly for
free-form objects; only the any-type branch is missing the namespace qualifier.

Suggest a fix

https://github.com/OpenAPITools/openapi-generator/blob/4aed9c1c635/modules/openapi-generator/src/main/resources/typescript-fetch/apis.mustache#L288

{{#isFreeFormObject}}runtime.anyToJSON{{/isFreeFormObject}}{{^isFreeFormObject}}{{{dataType}}}ToJSON{{/isFreeFormObject}}

Adding an isAnyType branch that also uses runtime.anyToJSON fixes it.

I have a patch with a regression test ready and will open a PR shortly.

Related issues/PRs

#1877 added anyToJSON and the isFreeFormObject branch. I could not find an existing report covering the
any-type case.