Sweep: Fix TypeScript + fetch generated code with `oneOf` to properly check the dto type

[sweep-ai[bot]]

Purpose

The purpose of this pull request is to fix an issue where the TypeScript + fetch generated code with oneOf does not properly check the dto type.

Description

The issue was that the generated instanceOfXXX() functions did not properly check the type property to determine which model instance it is. This caused bugs in production where Payload2 and Payload3 were never matched.

The changes in this pull request update the modelGeneric.mustache template to check if the type property matches the expected enum value for the model. This ensures that the instanceOfXXX() functions correctly identify the model instance.

Summary

• Updated the modelGeneric.mustache template to check the type property against the expected enum value for the model
• This ensures the instanceOfXXX() functions correctly identify the model instance when using oneOf
• Modified the instanceOfPayload1() function to check if the type property is equal to the first value in the Payload1TypeEnum

Fixes #1.

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Rollback Files For Sweep

• [ ] Rollback changes to modules/openapi-generator/src/main/resources/typescript-fetch/modelGeneric.mustache
• [ ] Rollback changes to modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/TypeScriptFetchClientCodegen.java

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[AnotiaWang]

The {{classname}}FromJSONTyped function should also be updated (near the if (json == null) condition)