XWIKI-18838: Use ARIA landmarks for main page regions

[Sereza7]

Jira: https://jira.xwiki.org/browse/XWIKI-18838
PR Changes:

• Added main landmarks on pages.

Notes:

• As of now, using the preview will create an accessibility violation (two main landmarks on the page, one inside an iframe in the other). AFAIK this is only on a few pages accessible by admins (e.g. color theme editing) so it's okay.
• The element that was used to be the main landmark depends on the templates, since we don't want to include breadcrumbs in it. Typically, it was either: set on the mainContentArea if it doesn't start with a "top breadcrumb", or set on a new DOM element that contains the title and the content of the page (without the breadcrumb).
• This PR is very much related to XWIKI-20696: Accessibility best-practice: use landmarks in view pages #2133 . The following views are made without the changes in the PR for XWIKI-20696. My solution for XWIKI-20696 as of now contains changes to the hierarchy macro and makes all breadcrumbs nav landmarks.

View:
Those screenshots were made with the landmark extension for Firefox.
You should look for the Main landmark indicated with a pink square on every screenshot

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[Sereza7]

Ready for review

PR Changes:

• Updated the test resources in xwiki-platform-tool-standards-validator

Note: Tests on the xwiki-platform-tool-standards-validator module after changes passed.

[michitux]

While I agree that it might be preferable to not to have the breadcrumbs in the main content I wonder if it is really a good idea to have on some pages <div id="mainContentArea"> while on others it is <main id="mainContentArea">. This creates quite an inconsistency that could lead to strange problems. Btw., I found this code which I think needs to be updated and also nicely highlights the problem with this inconsistency:

xwiki-platform/xwiki-platform-core/xwiki-platform-test/xwiki-platform-test-ui/src/main/java/org/xwiki/test/ui/po/BasePage.java

Line 603 in f472a03

.findElementWithoutWaiting(By.xpath("//div[@id = 'mainContentArea']/pre[contains(@class, 'xwikierror')]"))

Also, see #1667, I think it would be nice to have a consistent jump target for the skip header link. Maybe we should re-consider the decision to (not) include the breadcrumbs in the main content area.

[Sereza7]

Why we left the breadcrumb out of the main => https://forum.xwiki.org/t/accessibility-best-practice-landmarks/12051/10

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I think the best solution is to move the mainContentArea to systematically follow the main tag name. This could mess up a lot of Page object selectors in tests. Thinking a bit more about it, there was barely any trouble with page objects when adding the main, so it should be ~= the same and not that much to change.
Anyways, those changes in the tree structure become massive and I'll go through a series of tests and manual viewing to check that it doesn't break anything (typically going wherever I took the screenshots in the PR starting message).

[michitux]

As I've just found it, here is another comment saying that breadcrumbs shouldn't be part of the main content: w3c/aria-practices#1469 (comment).

[Sereza7]

PR Updates

• Removed the breadcrumbs from main on every template.
• Improved comments
• Homogenized changes

View

[michitux]

Looks good to me, but there is a conflict that prevents merging.