This makes it simpler for people to create new testchains in their own branches by removing the need to create a new static global variable for the new chains.
It also prepares chainparams and chainparamsbase to be cleaned out of globals by moving the globals and related functions (Params(), SelectParams(), etc) outside, maybe to globals/server.o and globals/common.o respectively.
But that would need another PR after this, something @theuni has been wanting to do for some time. I would prefer to do this first to be able to leave the 2 factories (which don’t need to depend on any global) where they are. Part of #6382