Change fortran header file extenstions from .h to .fh

[mcallic2]

Description
This changes the extension names from .h to .fh for fortran header files within FMS. It also changes any calls to the header files.

Fixes #1096

How Has This Been Tested?
Testes with autotools using oneapi and cmake
@rem1776 @underwoo

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• New check tests, if applicable, are included
• make distcheck passes

[rem1776]

just needs the doxygen fix i left the comment about in a few spots

[thomas-robinson]

@mcallic2 You need to link an issue for this.