[6.0] Router: Enforce suffix by default if enabled

[Hackwar]

Summary of Changes

This PR changes the feature introduced in 5.2.0 to be able to enforce a suffix ending if it is enabled and makes this the standard behavior. It removes the option from the SEF plugin and moves the code to the SiteRouter class, at the same time using the "tainted URL" feature from #44455 to prevent unnecessary redirects.

Testing Instructions

1. Enable SEF URLs with suffix ending.
2. Open a random URL of the site and remove the suffix
3. Open a random URL of the site and replace the suffix with something else and add ?format=html to the URL
4. Open a random URL of the site, remove the suffix and add ?format=html to the URL

Actual result BEFORE applying this Pull Request

Joomla loads all the URLs without any redirects.

Expected result AFTER applying this Pull Request

All URLs are redirected to the version with .html at the end.

Link to documentations

Please select:

• Documentation link for docs.joomla.org:

• No documentation changes for docs.joomla.org needed

• Pull Request link for manual.joomla.org:

• No documentation changes for manual.joomla.org needed

[HLeithner]

I have tested this item 🔴 unsuccessfully on 9873b77

* install pr

• install sample data
• open website blog entry "Welcome to our blog" (/blog/welcome-to-your-blog) in new tab and let it stay open
• change setting "Add Suffix to URL" to yes
• reload page opened before: 0 Call to undefined method Joomla\CMS\Router\SiteRouter::setTainted()

Expected a smooths transition, at least not a fatal error

#	Function	Location
1	()	JROOT/libraries/src/Router/SiteRouter.php:203
2	Joomla\CMS\Router\SiteRouter->parseFormat()	JROOT/libraries/src/Router/Router.php:384
3	Joomla\CMS\Router\Router->processParseRules()	JROOT/libraries/src/Router/Router.php:144
4	Joomla\CMS\Router\Router->parse()	JROOT/libraries/src/Application/SiteApplication.php:738
5	Joomla\CMS\Application\SiteApplication->route()	JROOT/libraries/src/Application/SiteApplication.php:243
6	Joomla\CMS\Application\SiteApplication->doExecute()	JROOT/libraries/src/Application/CMSApplication.php:306
7	Joomla\CMS\Application\CMSApplication->execute()	JROOT/includes/app.php:58
8	require_once()	JROOT/index.php:32
```<hr /><sub>This comment was created with the <a href="https://github.com/joomla/jissues">J!Tracker Application</a> at <a href="https://issues.joomla.org/tracker/joomla-cms/44480">issues.joomla.org/tracker/joomla-cms/44480</a>.</sub>

[Hackwar]

That is why it says "tainted URL" feature from #44455 and since that PR is not merged yet, this PR indeed fails.

[HLeithner]

I changed this to draft since it's not ready

[Hackwar]

I added the b/c break label because technically it removes anoption and forces this behavior on everyone, even though it is the expected behavior.