Improve the chapter navigation experience

[krilnon]

The book's chapters are divided into three parts: the Guided Tour, Language Guide, and Language Reference. As a result, the automatically generated See Also sections at the end of each chapter are fairly distracting (and obviated somewhat by DocC's new sidebar). We should consider adopting some proposed DocC improvements like @AutomaticSeeAlso(disabled) and @AutomaticPagination.

rdar://101885438

[amartini51]

As of swiftlang/swift-docc#368 we can now disable the automatic see-also and customize the "eyebrow" title. Automatic pagination looks like that's still future DocC work.

[amartini51]

I made a branch to try out the new DocC directives. Looks like we probably want to wait for @GlobalOptions to be implemented too, so we don't have to write the same options on every chapter.

https://github.com/amartini51/swift-book/tree/navigation_6