3rd attempt at trying to push view transition types examples

[chrisdavidmills]

I am currently working on documenting view transition types; this PR adds three examples that demonstrate various aspects of the feature.

I also took this opportunity to add an index page for the view transitions demos, and link to that instead from the readme file, thereby cleaning it up a bit and making them easier to navigate.

[pepelsbey]

Looks good! Thank you :)

A few suggestions:

• “MPA transition types example” and “MPA multiple transition types example” book demos look and behave identically but achieve it slightly differently. I would maybe highlight it in the folder’s index?

• For the same book demo: I would add chapter names to subpage titles to make it clear that we’re navigating between pages: “Chapter 1 — Table of contents MPA view transition types”, etc.

• Maybe we should use README.md for index pages? They are rendered to HTML. For example: fetch/README.md turns into https://mdn.github.io/dom-examples/fetch/ — this will make them easier to maintain.

[chrisdavidmills]

Looks good! Thank you :)

A few suggestions:

* “MPA transition types example” and “MPA multiple transition types example” book demos look and behave identically but achieve it slightly differently. I would maybe highlight it in the folder’s index?

* For the same book demo: I would add chapter names to subpage titles to make it clear that we’re navigating between pages: “Chapter 1 — Table of contents MPA view transition types”, etc.

* Maybe we should use README.md for index pages? They are rendered to HTML. For example: `fetch/README.md` turns into https://mdn.github.io/dom-examples/fetch/ — this will make them easier to maintain.

All done.

[github-actions]

This pull request has merge conflicts that must be resolved before it can be merged.

[pepelsbey]

Suggested change

	<li><a href="index3.html">Chapter 2</a></li>
	<li><a href="index3.html">Chapter 2</a></li>

Ouch, I just realized that naming in the demo is a bit confusing: Chapter 2 goes to index3.html.

I'm absolutely nitpicking here, but it would be nice to have a structure like that:

• index.html (Intro)
• chapter1.html
• chapter2.html
• etc.

I hope it won't be too much work to organize it little better. What do you think?

[chrisdavidmills]

Please take a look at the latest commit. I've updated the page titles so the pages are now "Chapter 1" to "Chapter 5" and removed the "Introduction" title, so the numbers match up.

I don't want to start changing the file names, as my JS logic relies on them, and that would be even more work to fix. I think this works.

[pepelsbey]

Perfect! Thank you :)

[chrisdavidmills]

Thanks so much, @pepelsbey, much appreciated.