[BUG][DART] API with path parameter named `format` produces incorrect paths.

Created by: tombowers

Bug Report Checklist

Have you provided a full/minimal spec to reproduce the issue?
Have you validated the input using an OpenAPI validator (example)?
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?
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Description

If a resource contains a path parameter named format, the generated library replaces the parameter with the word json prior to normal parameter substitution, breaking the API.

Here is an example of the code produced.

final path = '/things/{format}'.replaceAll('{format}', 'json')
    .replaceAll('{' + 'format' + '}', format.toString());

openapi-generator version

5.0.0 (also tested with 5.0.1-20210206.073348-97)

OpenAPI declaration file content or url

openapi: 3.0.4
info:
  title: Sample API
  version: 0.1.1
paths:
  /things/{format}:
    get:
      summary: Returns a list of things.
      parameters:
        - in: path
          name: format
          schema:
            type: string
          required: true
      responses:
        '200':
          description: A JSON array of things

Generation Details

Generated using compiled jar. e.g.

java -cp openapi-generator-cli-5.0.1-20210206.073348-97.jar org.openapitools.codegen.OpenAPIGenerator generate -i "format-issue.yml" -g dart -o formatissue

Suggest a fix

I am unfamiliar with the codebase, but it appears to be happening here. https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/resources/dart/api.mustache#L28

And it seems to be present in many languages, for example. https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/resources/android/api.mustache#L63