Issue: SPR-16612

Issue: SPR-16494

Issue: SPR-16548

Issue: SPR-16423

Issue: SPR-16422

Closes gh-1676

Issue: SPR-16394

Issue: SPR-16442

From:
  Thymeleaf
  Groovy Markup
  FreeMarker
  JSP & JSTL
  Script Views
  XML
  Tiles
  XSLT
  PDF, Excel
  RSS, Atom
  Jackson

To:
  Thymeleaf
  FreeMarker
  Groovy Markup
  Script views
  JSP & JSTL
  Tiles
  RSS, Atom
  PDF, Excel
  Jackson
  XML
  XSLT

Also move View Technologies after MVC Config to align order with
WebFlux config.

Issue: SPR-16393

1. The View Technologies chapter in Spring MVC
2. The View Resolution and View Resolver config in WebFlux

Issue: SPR-16393

Issue: SPR-16393

Issue: SPR-16203

We cover this more succinctly from other places, e.g. in Model Methods
by referring to the Javadoc of Contentions, or pointing to the
RequestToViewNameTranslator.

Issue: SPR-16040

Issue: SPR-16040

Issue: SPR-16040

Issue: SPR-16040

Issue: SPR-16040

Issue: SPR-16040

Cross-reference sections on HttpMessageReader/Writer and
HttpMessageConverter and improve the content.

Issue: SPR-16260

Issue: SPR-16240

A new HTTP/2 support section has been added in the Spring MVC
documentation. Also, a dedicated wiki page is created for specific
container support information.

Issue: SPR-15821

Issue: SPR-16087

Issue: SPR-16074

Issue: SPR-16041

Easier to find (at the top level) and better summary of testing support.
Improve structure headings names.
Remove or update outdated content.

Optimized for viewing in left TOC.