Fix Package task

[andyleejordan]

This now leaves the VSIX named as vsce creates it:
powershell-YYYY.MM.X.vsix, instead of renaming it PowerShell-Insiders.vsix.
I can't think of anything this would break, since the upload is not actually
done with the deleted Upload task but with an ADO pipeline task.

This also fixes the path to InvokePesterStub.ps1 which is now part of the
PowerShellEditorServices repository. This was necessary in order to sign it, as
it must be signed before the VSIX is created. Moving it to the other repo was
the best way to solve the "chicken-egg" problem that presented.

Resolves #3293 and combined with PowerShell/PowerShellEditorServices#1513, resolves #2536.

[andyleejordan]

@rjmholt Running a "release" to see if everything still works.

[andyleejordan]

Oof, ok so this doesn't quite work. It's a chicken-egg problem. We need InvokePesterStub.ps1 signed before the build happens, so that it can go into the resulting VSIX, which itself then needs signing. Grr.

[andyleejordan]

@andys-mac-mini ~/src/vscode-powershell andschwa/package-fix ≡
> . '/Users/andschwa/.vscode/extensions/ms-vscode.powershell-2021.6.2/modules/PowerShellEditorServices/InvokePesterStub.ps1' -ScriptPath '/Users/andschwa/src/PowerShellEditorServices/test/PowerShellEditorServices.Test.Shared/Symbols/PesterFile.tests.ps1' -All -Output 'FromPreference'

Importing Pester module...
WARNING: Failed to import Pester. You must install Pester module to run or debug Pester tests.
WARNING: You can install Pester by executing: Install-Module Pester -Scope CurrentUser -Force
PS> Install-Module Pester -Scope CurrentUser -Force

@andys-mac-mini ...itorServices.Test.Shared/Symbols andschwa/import-pester-stub ≡                                                            > . '/Users/andschwa/.vscode/extensions/ms-vscode.powershell-2021.6.2/modules/PowerShellEditorServices/InvokePesterStub.ps1' -ScriptPath '/Users/andschwa/src/PowerShellEditorServices/test/PowerShellEditorServices.Test.Shared/Symbols/PesterFile.tests.ps1' -All -Output 'FromPreference'                                                                                                                                                                                                                                                                                        
Importing Pester module...

Starting discovery in 1 files.
Discovery finished in 188ms.
Running tests.
[+] /Users/andschwa/src/PowerShellEditorServices/test/PowerShellEditorServices.Test.Shared/Symbols/PesterFile.tests.ps1 507ms (33ms|317ms)
Tests completed in 528ms
Tests Passed: 3, Failed: 0, Skipped: 0 NotRun: 0
PS>