Filenames incorrect on windows due to inconsistent use of "/" and File.separator [Windows only, Jersey JAX-RS]

As of 1.0.17, becuase the DefaultCodegenConfig#apiFilename method uses File.separator to concatenate the filename, an issue occurs on windows that causes the generator to create files with incorrect package structures. This is a problem because some classes are expected to be in the same package, and this could also break ignore rules, leading to duplicate classes and other compilation issues. In the java JAX-RS generator, we check for a '/', causing the index to be inaccurate on Windows (or any other OS that doesn't use / as the file path separator), resulting in a the substring and replace calls not doing what is intended. The same happens in the Factory.mustache branch of the if statement.

We should use File.separator everywhere we are forming/checking file paths. Otherwise, we run the risk of assuming the OS the project is running on, and breaking compilation due to malformed paths.

Start with DefaultCodegenConfig.java at apiFilename and AbstractJavaJAXRSServerCodegen.java around line 227. Inspect the Factory.mustache branch as well, tracing where '/' is used while constructing or parsing paths. Done means path handling consistently uses File.separator and generated Windows package structures, ignore rules, and filenames no longer cause duplicate classes or compilation issues.