added enzyme.i and necessary changes to build

[sshiraiwa]

This PR add minimum changes to fix --mfem-branch=master build failure after enzyme.hpp was added. It also includes:

• MFEM version used in default build is change to the version from Nov. 30 2023.
• Fixed ex26 and ex26p to use the constrained prolongation operator
• Added a wrapper to Array< Array *> : Array to intArray