Relocate spack_cmd and scripts from installer to root bin (#24651)

Relocate spack_cmd and scripts from installer
to root bin

Refactor documentation, installer, and launcher
to facilitate that change

bin/haspywin.py

@@ -0,0 +1,20 @@
+# Copyright 2013-2021 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+import subprocess
+import sys
+
+
+def getpywin():
+    try:
+        import win32con  # noqa
+    except ImportError:
+        subprocess.check_call(
+            [sys.executable, "-m", "pip", "-q", "install", "--upgrade", "pip"])
+        subprocess.check_call(
+            [sys.executable, "-m", "pip", "-q", "install", "pywin32"])
+
+
+if __name__ == '__main__':
+    getpywin()