refactor: limit magic paths use

[kdrienCG]

This PR reduces the use of magic paths to access common objects for developers ("/Problem/domain/", "/Problem/domain/Constitutive", "/Problem/Events/", etc)

It introduces a GlobalViewKeys struct to provide a centralized definition of the names of these common objects.

It also adds a ProblemManagerBase lightweight interface over the ProblemManager that gives typed access to these objects without requiring to bring the full ProblemManager

---

Example of its use:

Group & problemManager = this->getGroupByPath( "/Problem" );
Group & physicsSolverManager = problemManager.getGroup( "Solvers" );

is replaced by:

PhysicsSolverManager & physicsSolverManager = getProblemManagerBase( *this ).getPhysicsSolverManager();