Performance for gutenberg blocks on post detail pages

[menno-ll]

We have projects where it seems that the more blocks we add, the slower the project gets.
And when I did run qcachegrind on a project experiencing performance issues, 1 thing stood out.

What stands out is that there seems to be some space to gain if in Block_Manager.php determine_block_type_class we would do less calls to class_exists().
What i guess we can do is add a static property, or make the class a singleton.
Then, we can maybe use some local caching to not have to do this check for every block.
As well that we then will skip the other filters as well, adding extra potential slowdowns.