v3: Support for external MAPL library

This release of v3 adds support for building GEOSgcm, et al, with MAPL as an external library rather than internal. This could be useful for Spack builds of GEOSgcm where they want to use a prebuilt MAPL.

Also, backport some updates from main.

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From CHANGELOG.md

Changed

• Support for building GEOSgcm with Spack using MAPL as library
  • Update esma_create_stub_component to look for mapl_stub.pl in $MAPL_BASE_DIR/etc (which is a variable defined by ecbuild)
  • Update esma_generate_automatic_code to look for mapl_acg.pl in $MAPL_BASE_DIR/etc (which is a variable defined by ecbuild)
  • Require CMake 3.18 for features used in above updates
• Backport fixes from main
  • More support for NVHPC
  • Support for Hygon processors with GNU Fortran
• Update to CircleCI orb v4

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What's Changed

• v3: Support for MAPL-as-library by @mathomp4 in #404

Full Changelog: v3.51.0...v3.52.0