Add a Syntax Registry

Goal: Remove the static hard-coded registration of Syntaxes from rendering-api and move the syntax registration in each syntax module or in extensions.

Need example: The MD extension cannot change the pretty name of the markdown/1.2 syntax ATM since the Rendering CTS is using Syntax.valueOf() to convert the markdown/1.2 syntax id into a Syntax object and while doing so the pretty name is lost and thus the MD extension tests are failing.