XRENDERING-613: RenderingContextStore should not call RenderingContext#getTargetSyntax() when it does not need the value

  * Fix wrong condition that has been introduced because of a bad test
    input
  * Add a new test to assess the correct expectation

* Was still not working...

* Fix initialization to handle core Syntax Provider components

* Fix bug about the wrong Type being used
* Register more syntaxes to the syntax registry
* Removed more usages of the old Syntax.* static syntaxes

* Replace more deprecation calls to Syntax.valueOf() with calls to the Syntax Registry

* Remove deprecated call

* Replace more deprecation calls to Syntax.valueOf() with calls to the Syntax Registry
* Convert test to JUnit5/Mockito

* Fix test

[misc] Only allow xwiki-rendering build to get dependencies/plugins from Maven Central and XWiki own snapshots

Currently translated at 20.0% (1 of 5 strings)

Translation: XWiki Rendering/Content Macro
Translate-URL: https://l10n.xwiki.org/projects/xwiki-rendering/content-macro/si/