Update the minimum VTK-m to 2.1

VTK-m 2.1 contains some important features to support reading and writing
vector fields of different sizes. FIDES is updated to require this newer
version to take advantage of these features.

CMakeLists.txt

@@ -27,8 +27,9 @@ if (ADIOS2_VERSION VERSION_GREATER_EQUAL "2.8.0")
   set(ADIOS_DEFS FIDES_ADIOS_HAS_RANDOM_ACCESS)
 endif()
 
-# need to continue to support v1.9 for awhile
-find_package(VTKm REQUIRED)
+# Minimum VTK-m version is 2.1. Future versions of VTK-m should maintain
+# backward compatibility.
+find_package(VTKm 2.1 REQUIRED)
 
 if (VTKm_ENABLE_CUDA)
   enable_language(CUDA)

docs/dev/changelog/update-vtkm-version.md

+## Update the minimum VTK-m to 2.1
+
+VTK-m 2.1 contains some important features to support reading and writing
+vector fields of different sizes. FIDES is updated to require this newer
+version to take advantage of these features.