fix(graphql-server): Move yoga creation to avoid creation on every re…

…quest (#9039)

**Problem**
v6 has seen some performance issues. These appear to have sneaked in on
#8339. This just reverts the change by moving the creation of the yoga
object so that it isn't created on every request.

**Changes**
1. Moves yoga creation.

**Outstanding**
1. We still have a tiny bit of work to do analysing a slight performance
decline since 4.4.3