Old Java doc (as generated by the original javadoc tool which also inspired other languages I believe) had the kind of navigation you're looking for - it was a

Old Java doc (as generated by the original javadoc tool which also inspired other languages I believe) had the kind of navigation you're looking for - it was a boxy HTML frame-based layout so it had to go, but I'm not sure why the default javadoc theme dropped in-page method navigation altogether.