Make "Index" a reserved word (OpenAPITools#6000)

Some APIs have a model called "Index" which would create a file
"Index.ts" which would override "index.ts" on case-insensitive file
systems (e.g. macOS, some Windows versions). Make "Index" a reserved
word to prevent this clash.

Author: haraldF

docs/generators/typescript-fetch.md

@@ -76,6 +76,7 @@ sidebar_label: typescript-fetch
 <li>HTTPHeaders</li>
 <li>HTTPMethod</li>
 <li>HTTPQuery</li>
+<li>Index</li>
 <li>JSONApiResponse</li>
 <li>Middleware</li>
 <li>ModelPropertyNaming</li>

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/TypeScriptFetchClientCodegen.java

@@ -327,6 +327,9 @@ private void addExtraReservedWords() {
         this.reservedWords.add("VoidApiResponse");
         this.reservedWords.add("BlobApiResponse");
         this.reservedWords.add("TextApiResponse");
+        // "Index" would create a file "Index.ts" which on case insensitive filesystems
+        // would override our "index.js" file
+        this.reservedWords.add("Index");
     }
 
     private boolean getUseSingleRequestParameter() {