Improve readability of documentation and support for UHD and ultrawide monitors

[Splaktar]

Here are some screenshots from near UHD / wide screen displays. While the guides have a max-width, I think that we can do better. However the Overviews, API docs, and Examples have no max-width and are not very readable on a wide screen.

Related issues

• set max line length for content area of documentation angular#24707 recommends aligning with documentation studies that show a max line length of ~75 characters is the most readable.
• aio: Consider implementation of max-wid centered content concept for documentation pages angular#22246

Screenshots

Guides

[Splaktar]

This was implemented in AIO recently and the reception from developers has been extremely positive.