Initial contribution of LibPressio ecosystem (#32630)

* Add libpressio and dependencies; some of these packages are
  maintained as forks of the original repositories and in those
  cases the docstring mentions this.
* Add optional dependency in adios2 on libpressio
* cub package: set CUB_DIR environment variable for dependent
  installations
* Clear R_HOME/R_ENVIRON before Spack installation (avoid sources
  outside of Spack from affecting the installation in Spack)
* Rename dlib to dorian3d-dlib and update dependents; add new dlib
  implementation. Pending an official policy on how to handle
  packages with short names, reviewer unilaterally decided that
  the rename was acceptable given that the new Spack dlib package
  is referenced more widely (by orders of magnitude) than the
  original

Co-authored-by: Samuel Li <shaomeng@users.noreply.github.com>

lib/spack/spack/build_environment.py

@@ -201,6 +201,8 @@ def clean_environment():
 
     env.unset("CMAKE_PREFIX_PATH")
     env.unset("PYTHONPATH")
+    env.unset("R_HOME")
+    env.unset("R_ENVIRON")
 
     # Affects GNU make, can e.g. indirectly inhibit enabling parallel build
     # env.unset('MAKEFLAGS')