move fix to #10567 into website postprocessor

[cderv]

Fixes #11596

This PR does the canonicalizeTitlePostprocessor() into website post processor only which avoid any undesired DOM modification on non website project.

I think we should look into canonicalizeTitlePostprocessor() because it does think for website without checking some assumption

• it fixes breadcrumbs that only are done in bootstrap format. So possibly the fix should be done in websiteNavigationExtras() which applies only in bootstrap
• It does try to create a title block and move the title into it, but it does not really do it considering the check on the title. Also it used classes (like quarto-title-banner) that are only used in some specific situation (in the example when title-block-banner is set).

I'll suggest we look in all that more closely for 1.7 and adapt the fix for #10567 in a more generic way (make h1 and no title equivalent to title).

[cderv]

Changelog done in 1.6 for regression fix through

• Fix regression that appeared for non website regarding h1 canonicalization #11640

The change for the regression have been simplified

[cderv]

Let's merge so that pkgdown problem can be solved