Adding basic Windows features (#21259)

* Snapshot of some MSVC infrastructure added during experiments a while ago.  Rebasing from spack/develop.

* Added platform and OS definitions for Windows.

* Updated Windows platform file to conform to new archspec use.

* Added Windows as a platform; introduced some debugging code.

* Added type annotations.

* Fixed copyright.

* Removed print statements.

* Ensure `spack arch` returns correctly on Windows (#21428)

* Correctly identify windows as 'windows-Windows10-AMD64'

lib/spack/env/cc

@@ -241,7 +241,7 @@ case "$command" in
         mode=cpp
         debug_flags="-g"
         ;;
-    cc|c89|c99|gcc|clang|armclang|icc|icx|pgcc|nvc|xlc|xlc_r|fcc|amdclang)
+    cc|c89|c99|gcc|clang|armclang|icc|icx|pgcc|nvc|xlc|xlc_r|fcc|amdclang|cl.exe)
         command="$SPACK_CC"
         language="C"
         comp="CC"