refactor powershell setup to make it sourceable (#29987)

* refactor powershell setup to make it sourceable

* only set editor if it is unset

* change directory to spack root in subshell

* Update share/spack/setup-env.ps1

Co-authored-by: John W. Parent <45471568+johnwparent@users.noreply.github.com>

Co-authored-by: John W. Parent <45471568+johnwparent@users.noreply.github.com>

share/spack/setup-env.ps1

@@ -0,0 +1,61 @@
+# Copyright 2013-2022 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)
+
+Push-Location $PSScriptRoot/../..
+$Env:SPACK_ROOT = $PWD.Path
+Push-Location $PWD/..
+$Env:spackinstdir = $PWD.Path
+Pop-Location
+
+Set-Variable -Name python_pf_ver -Value (Get-Command -Name python -ErrorAction SilentlyContinue).Path
+
+# If python_pf_ver is not defined, we cannot find Python on the Path
+# We next look for Spack vendored copys
+if ($null -eq $python_pf_ver)
+{
+    $python_pf_ver_list = Resolve-Path -Path "$PWD\Python*"
+    if ($python_pf_ver_list.Length -gt 0)
+    {
+        $py_path = $python_pf_ver_list[$python_pf_ver_list.Length-1].Path
+        $py_exe = "$py_path\python.exe"
+    }
+    else {
+        Write-Error -Message "Python was not found on system"
+        Write-Output "Please install Python or add Python to the PATH"
+    }
+}
+else{
+    Set-Variable -Name py_exe -Value $python_pf_ver
+}
+
+if (!$null -eq $py_path)
+{
+    $Env:Path = "$py_path;$Env:Path"
+}
+
+if (!$null -eq $py_exe)
+{
+    Invoke-Expression "$py_exe $Env:SPACK_ROOT\bin\haspywin.py"
+    Invoke-Expression "$py_exe $Env:SPACK_ROOT\bin\spack external find python" | Out-Null
+}
+
+$Env:Path = "$Env:SPACK_ROOT\bin;$Env:Path"
+if ($null -eq $Env:EDITOR)
+{
+    $Env:EDITOR = "notepad"
+}
+
+
+Write-Output "*****************************************************************"
+Write-Output "**************** Spack Package Manager **************************"
+Write-Output "*****************************************************************"
+
+function global:prompt
+{
+    $pth = $(Convert-Path $(Get-Location)) | Split-Path -leaf
+    "[spack] PS $pth>"
+}
+Pop-Location
+