Extension methods from use of @ExtensionSource are not recognized in IJ

[rsmckinney]

Separated from #62:

Extension methods from use of @ExtensionSource are not recognized in IJ.

For example, this works as expected:

@Extension
public class PathExt {
    public static Stream<Path> list(@This Path path) throws IOException {
        return Files.list(path);
    }
}

Paths.get("").list().forEach(Path::isAbsolute);

However, when using @ExtensionSource, compilation still succeeds, but IntelliJ reports an error:

@ExtensionSource(source = Files.class)
@Extension
public class PathExt { }

// IntelliJ error: Cannot resolve method 'list' in 'Path'
// 'p' is also not resolved as a Path type, resulting in an additional error: Cannot resolve method 'isDirectory()'
Paths.get("").list().forEach(p -> System.out.println(p.isDirectory()));

[EotT123]

@rsmckinney This is resolved in #72