feat(fmi): support binary grid file

[wpbonelli]

Support an optional GWFGRID entry in FMI for the flow model's binary grid file. If provided, check the grids have the same size and idomain like we do in EXG as of #2149. This makes for the same error-checking in the exg (coupled) and fmi (post-processing) cases.

@langevin-usgs suggested making the grid file entry optional for some time (1-2 releases), then beginning to require it. At which point the reader could be modified to load the full dis, and we could consolidate these haphazard checks into a robust grid comparison as suggested by @mjr-deltares.

The grb file reader in zonebudget is moved to a new GridFileReader module in the main src dir. The reader now loads headers and builds an index at init time, after which variables can be read as necessary.

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Checklist of items for pull request

• Replaced section above with description of pull request
• Added new test or modified an existing test
• Formatted new and modified Fortran source files with fprettify
• Added doxygen comments to new and modified procedures
• Updated meson files, makefiles, and Visual Studio project files for new source files
• Updated definition files
• Updated develop.tex with a plain-language description of the bug fix, change, feature; required for changes that may affect users
• Updated input and output guide
• Removed checklist items not relevant to this pull request

[langevin-usgs]

Looks good.