Reorganize example documentation (#11757)

* Reorganize example documentation

This commit reorganizes example documentation in our online
documentation. The main changes here are:

* Chapter-per-lan

Reorganize example documentation (#11757)

* Reorganize example documentation

This commit reorganizes example documentation in our online
documentation. The main changes here are:

* Chapter-per-language is now removed in favor of tabs-in-a-page for
avoiding having the book be so large. Tabs are made with [mdbook-langtabs].
* Language-specific pages are all consolidated into a single page.
* Language-specific documentation now only mentions where to find docs
instead of trying to document an intro for each language here.
* "Further examples" was folded into the main API section, meaning we
just have one chapter of a lot of examples.

The main goal is to make the book less overwhelming from an example
perspective and ideally make it a bit easier to discover things. The
langtabs plugin is nice but not perfect, e.g. it doesn't support
`#`-anchors nor remembers which language you were looking at. Overall
though I feel this is still better than before.

[mdbook-langtabs]: https://github.com/nx10/mdbook-langtabs

* Fix typos

* Remove testing of mdbook from CI

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