PR Summary

Make Start-PSPackage give a better message about how to fix files.wxs
Some minor changes:

1. Avoid relative paths as much as possible.
2. Add a message about how to fix files.wxs when current files don't match the existing files.wxs.
3. Fix a few script analyzer warnings since I'm on it.

The messages before this PR: (relative paths)

PS:137> Start-PSPackage -Type msi
Packaging RID: 'win7-x64'; Packaging Configuration: 'Release'
Packaging Source: 'E:\PowerShell\src\powershell-win-core\bin\Release\netcoreapp2.1\win7-x64\publish'
Packaging Type: msi
verifying no new files have been added or removed...
WARNING: {$(env.ProductSourcePath)\sos_amd64_amd64_4.6.26814.04.dll} is no longer in product and should be removed from {E:\PowerShell\tools\packaging\..\..\assets\Files.wxs}
WARNING: new file in {$(env.ProductSourcePath)} with name {sos_amd64_amd64_4.6.26814.03.dll} in a {DirectoryRef} need to be added to {E:\PowerShell\tools\packaging\..\..\assets\Files.wxs}
Update xml saved to C:\Users\dongbow\AppData\Local\Temp\chov3oyp.3oi.xml
Current files to not match  {E:\PowerShell\tools\packaging\..\..\assets\Files.wxs}
At E:\PowerShell\tools\packaging\packaging.psm1:2721 char:9
+         throw "Current files to not match  {$FilesWxsPath}"
+         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo          : OperationStopped: (Current files t...sets\Files.wxs}:String) [], RuntimeException
+ FullyQualifiedErrorId : Current files to not match  {E:\PowerShell\tools\packaging\..\..\assets\Files.wxs}

The message with this PR: (resolved paths)

PS:139> Start-PSPackage -Type msi
Packaging RID: 'win7-x64'; Packaging Configuration: 'Release'
Packaging Source: 'E:\PowerShell\src\powershell-win-core\bin\Release\netcoreapp2.1\win7-x64\publish'
Packaging Type: msi
verifying no new files have been added or removed...
WARNING: {$(env.ProductSourcePath)\sos_amd64_amd64_4.6.26814.04.dll} is no longer in product and should be removed from {E:\PowerShell\assets\Files.wxs}
WARNING: new file in {$(env.ProductSourcePath)} with name {sos_amd64_amd64_4.6.26814.03.dll} in a {DirectoryRef} need to be added to {E:\PowerShell\assets\Files.wxs}
Updated xml saved to C:\Users\dongbow\AppData\Local\Temp\prumscbt.xax.wxs.
If component files were intentionally changed, such as due to moving to a newer .NET Core runtime, update 'E:\PowerShell\assets\Files.wxs' with the content from 'C:\Users\dongbow\AppData\Local\Temp\prumscbt.xax.wxs'.
Current files to not match  {E:\PowerShell\assets\Files.wxs}
At E:\PowerShell\tools\packaging\packaging.psm1:2724 char:9
+         throw "Current files to not match  {$FilesWxsPath}"
+         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo          : OperationStopped: (Current files t...sets\Files.wxs}:String) [], RuntimeException
+ FullyQualifiedErrorId : Current files to not match  {E:\PowerShell\assets\Files.wxs}

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Change is not breaking
• Make sure all .h, .cpp, .cs, .ps1 and .psm1 files have the correct copyright header
• This PR is ready to merge and is not Work in Progress.
  • If the PR is work in progress, please add the prefix WIP: to the beginning of the title and remove the prefix when the PR is ready.
• User-facing changes
  • Not Applicable
  • OR
  • User-facing Documentation needed
    • Issue filed - Issue link:
• Testing - New and feature
  • Not Applicable or can only be tested interactively
  • OR
  • Make sure you've added a new test if existing tests do not effectively test the code changed
    • Add [feature] if the change is significant or affects feature tests