wrap-java: Handle generic parameter replacement in inherited methods

[sidepelican]

This PR is part of the improvements for #599.

Currently, generating code for JavaUnaryOperator results a compilation error.

.../JavaUnaryOperator.swift:14:36: error: cannot find type 'R' in scope
12 |   /// ```
13 |   @JavaMethod(typeErasedResult: "R!")
14 |   public func apply(_ arg0: T?) -> R!
   |                                    `- error: cannot find type 'R' in scope
15 | 
16 |   /// Java method `compose`.

In Java, Function<T, R> has two type parameters, but UnaryOperator<T> extends it by mapping both to a single type T.
wrap-java does not have a mechanism to substitute these generic parameters during inheritance, it incorrectly use R.

I have introduced a SubstitutionMap to track and apply generic parameter replacements during type resolution.

[ktoso]

Nice work :)