Replaced the use of pointers by allocatables in function arguments and local variables

Description

Replace the use of pointers by allocatables in function arguments and local variables. Also removed the pointer attribute from some type components and some global variables.

News snippet

Replaced the use of pointers by allocatables in function arguments and local variables.

Checklist

• I have checked that my code follows the Octopus coding standards
• I have added tests for all the new features added in this request.