[BUG] Duplicate model files generated using typescript-angular for schema objects with the same name/different casing

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?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

Given schema definitions that use the same name with different casing (e.g. MySchema and mySchema) the generated model for typescript does not differentiate and only my-schema.ts is generated.

We also noticed that using fileNaming=camelCase (the default value) results in mySchema.ts and mYSchema.ts both containing the same contents even though you'd expect different based on the schema example below. The generated interface is MySchema in both files which is also problematic.

openapi-generator version

6.4.0 and same result with 7.8.0

OpenAPI declaration file content or url

openapi: 3.0.1
info:
  title: OpenAPI definition
  version: v0
paths:
  /fake/endpoint:
    get:
      responses:
        "200":
          content:
            application/json:
              schema:
                type: object
          description: OK
components:
  schemas:
    MySchema:
      type: object
      properties:
        prop1:
          type: string
    mySchema:
      type: object
      properties:
        prop2:
          type: string
    MYSchema:
      type: object
      properties:
        prop3:
          type: string

Generation Details

Generated content:

issue-repro-api/src/genfiles
└── openapi
    ├── README.md
    ├── api
    │   └── api.ts
    ├── api.module.ts
    ├── configuration.ts
    ├── encoder.ts
    ├── git_push.sh
    ├── index.ts
    ├── model
    │   ├── models.ts
    │   └── my-schema.ts
    ├── param.ts
    └── variables.ts

model.ts content

export * from './my-schema';
export * from './my-schema';

my-schema.ts content

export interface MySchema { 
    prop2?: string;
}

Generator output indicates it is overriting my-schema.ts is being written 2 times but I would have expected 3 times. given the example above.

...
[main] INFO  o.o.codegen.TemplateManager - writing file issue-repro-api/src/genfiles/openapi/model/./my-schema.ts
[main] INFO  o.o.codegen.TemplateManager - writing file issue-repro-api/src/genfiles/openapi/model/./my-schema.ts

Steps to reproduce

openapi-generator-cli generate \
  -i openapi.yml \
  -g typescript-angular \
  -o src/genfiles/openapi \
  --additional-properties \
    providedIn=none,\
    ngVersion=13.3.9,\
    supportsES6=true,\
    withInterfaces=true,\
    fileNaming=kebab-case,\
    enumPropertyNaming=UPPERCASE,\
    removeEnumValuePrefix=false,\
    apiModulePrefix=IssueRepro,\
    useSingleRequestParameter=true,\
    stringEnums=true

Related issues/PRs

Didn't find any.

Suggest a fix

Might require multiple fixes related to a case-sensitive mode for all code generation, to avoid converting specs to kebab and camel cases when that can cause issues like these.

Ideally the example spec would result in MySchema.ts, mySchema.ts and MYSchema.ts each with an interface that has case sensitive names.

Start by running the provided OpenAPI declaration with the typescript-angular generator command and compare the generated model files and exports. Trace the naming and file-writing behavior shown in the generation output, then verify that MySchema, mySchema, and MYSchema produce distinct files, interfaces, and exports without overwriting.