[BUG] [JAVA] Schema Mapping with generics skips wrong path, fails with file error on windows

Bug Report Checklist

[x] Have you provided a full/minimal spec to reproduce the issue?
[x] Have you validated the input using an OpenAPI validator (example)?
[x] Have you tested with the latest master to confirm the issue still exists?
[x] Have you searched for related issues/PRs?
[x] What's the actual output vs expected output?

Description

When I specify a schema mapping (aka schemaMappings map in a config.yaml), where the mapped value contains a java type with generic parameters (e.g. Wrapper<Thing>), then the code generation aborts with

Exception in thread "main" java.lang.RuntimeException: Could not process model 'ThingWrapper'.Please make sure that your schema is correct!
[...]
Caused by: java.nio.file.InvalidPathException: Illegal char <<> at index 53: .\src\main\java\org\openapitools\client\model\Wrapper<Thing>.java

at https://github.com/OpenAPITools/openapi-generator/blob/2abcb4f7f0aa67c126304e43602ae72a83f2dca7/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultGenerator.java#L491

openapi-generator version

At least since 7.4.0, still broken on master

OpenAPI declaration file content or url

https://gist.github.com/Xiphoseer/05c1b92d36ff3beef1e7e84fc476ccf9

Generation Details

Java Codegen, but applies to all DefaultCodegen where toModelFilename resolves schemaMappings
Uses schemaMappings

Steps to reproduce

Save api.yaml and config.yaml in a directory
Run openapi-generator-cli generate -c .\config.yaml

It's possible / likely this particular error only occurs on windows, Linux will let me create a file with < in the name just fine, but my understanding is that just hides the underlying issue.

Related issues/PRs

None found

Suggest a fix

I'd suggest removing the entire loop marked as "HACK": https://github.com/OpenAPITools/openapi-generator/blob/2abcb4f7f0aa67c126304e43602ae72a83f2dca7/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultGenerator.java#L488-L493

It doesn't quite do what it's supposed to (skip generation of model templated files for models that are schema mapped), because toModelFilename for Java calls toModelName which considers schemaMappings and thus acts on the mapped model name and file, not the file it would generate without the schema mapping. Additionally, the function where this happens seems to ensure anyway (using continue after the loop) that the schema will not be imported for generation.

This overload in AbstractJavaCodegen is what causes the issue, but it is a valid implementation since Java does require the class and file name to match: https://github.com/OpenAPITools/openapi-generator/blob/2abcb4f7f0aa67c126304e43602ae72a83f2dca7/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaCodegen.java#L930-L933

The default implementation is not susceptible to this because it's stateless: https://github.com/OpenAPITools/openapi-generator/blob/2abcb4f7f0aa67c126304e43602ae72a83f2dca7/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java#L1637-L1639

So far I did not reason about the other generators.

OpenAPITools / openapi-generator