[Dart] Make clients crossplatform

Created by: nickmeinhold

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh, ./bin/openapi3/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\. If contributing template-only or documentation-only changes which will change sample output, be sure to build the project first.
• Filed the PR against the correct branch: master, 4.1.x, 5.0.x. Default: master.
• Copied the technical committee to review the pull request if your PR is targeting a particular programming language.
  • @ircecho @swipesight @jaumard

Description of the PR

Since 12.0 the http package has had conditional imports so creating a Client() will use the appropriate option of either a BrowserClient or an IOClient depending on the platform so there would seem to be no need for the generator to use a browserClient flag to distinguish between Flutter and the web.

I didn't create an issue as there was already #3540 (closed) (although it's been closed so I wasn't sure what I should do).

modules/openapi-generator/src/main/resources/dart2/api_client.mustache

@@ -10,7 +10,7 @@ class QueryParam {
 class ApiClient {
 
   String basePath;
-  var client = {{#browserClient}}Browser{{/browserClient}}Client();
+  var client = Client();
 
   Map<String, String> _defaultHeaderMap = {};
   Map<String, Authentication> _authentications = {};

modules/openapi-generator/src/main/resources/dart2/apilib.mustache

 library {{pubName}}.api;
 
 import 'dart:async';
-import 'dart:convert';{{#browserClient}}
-import 'package:http/browser_client.dart';{{/browserClient}}
+import 'dart:convert';
 import 'package:http/http.dart';
 
 part 'api_client.dart';

modules/openapi-generator/src/main/resources/dart2/pubspec.mustache

@@ -4,6 +4,6 @@ description: {{pubDescription}}
 environment:
   sdk: '>=2.0.0 <3.0.0'
 dependencies:
-  http: '>=0.11.1 <0.13.0'
+  http: '>=0.12.0 <0.13.0'
 dev_dependencies:
   test: ^1.3.0

samples/client/petstore/dart/flutter_petstore/openapi/.openapi-generator/VERSION

-4.1.0-SNAPSHOT
\ No newline at end of file
+4.1.1-SNAPSHOT
\ No newline at end of file

samples/client/petstore/dart/flutter_petstore/openapi/docs/PetApi.md

@@ -151,7 +151,7 @@ Name | Type | Description  | Notes
 [[Back to top]](#) [[Back to API list]](../README.md#documentation-for-api-endpoints) [[Back to Model list]](../README.md#documentation-for-models) [[Back to README]](../README.md)
 
 # **findPetsByTags**
-> List<Pet> findPetsByTags(tags, maxCount)
+> List<Pet> findPetsByTags(tags)
 
 Finds Pets by tags
 
@@ -165,10 +165,9 @@ import 'package:openapi/api.dart';
 
 var api_instance = PetApi();
 var tags = []; // List<String> | Tags to filter by
-var maxCount = 56; // int | Maximum number of items to return
 
 try { 
-    var result = api_instance.findPetsByTags(tags, maxCount);
+    var result = api_instance.findPetsByTags(tags);
     print(result);
 } catch (e) {
     print("Exception when calling PetApi->findPetsByTags: $e\n");
@@ -180,7 +179,6 @@ try {
 Name | Type | Description  | Notes
 ------------- | ------------- | ------------- | -------------
  **tags** | [**List&lt;String&gt;**](String.md)| Tags to filter by | [default to []]
- **maxCount** | **int**| Maximum number of items to return | [optional] [default to null]
 
 ### Return type