Move the exchange operator related code in a separate file and add support for CAM functionals

Description

• Move the exchange operator related code in a separate file.
• Add the support for cam functionals.
• Add the support for the MVORD functionals.

This merge request is part of the merge for hybrids functionals in solids.

News snippet

Improved support of hybrid functionals. Add support for CAM and MVORB functionals.

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.