Support ConstrainedLanguage mode

[TylerLeonhardt]

With this PR, we have some support of ConstrainedLanguage mode. The LanguageMode is inherited from the initial runspace that starts Start-EditorServices

Windows PowerShell is started without PSRL and it is working... but there's more work that will need to be done here. Here are notes I've made from this:

• Custom Clear-Host doesn't work... probably because $psEditor doesn't work
  • Fixed by only calling $psEditor.....Clear() on FullLanguage
• $psEditor doesn't work because of method invoking
  • ISE has same problem... aka by-design
• Diagnostics aren't showing up (on Windows PowerShell, but show up on PSCore probably because of different definitions of "Trusted")
  • PSSA is being loaded with ConstrainedLanguage mode in Windows PowerShell to this proves my theory.
• Windows PowerShell is started without PSRL (this is also happening in a console outside of VS Code)
  • NOTE: idk why but PSReadLine doesn't show up in Get-Module -list in Windows PowerShell
  • Since we won't offer PSRL for ConstrainedLanguage mode initially, this isn't a problem atm
• PS 6.2+ loads PSRL... and it seems to work (syntax highlighting, readline all works)... but it emits a System.NotSupportedException: Cannot dot-source this command because it was defined in a different language mode... over and over and over so not sure if it's PSRL's fault or PSES's yet...
  • For now, I'm offering the legacy readline for ConstrainedLanguage mode.
• debugging does not work
  • The file is run, but the setting of breakpoints fails silently. I think this is ok for now... ideally we put up a warning... but that's hard to do from the DebugServer.
• Expand Alias doesn't work
  • waiting on Introduce Get-EditorServicesParserAst to expand on ExpandAlias #1199

[TylerLeonhardt]

This is now a "Support ConstrainedLanguage mode" PR... Ultimately:

• PSRL doesn't work fully
• Debugging runs the code but breakpoints don't work
  we could say debugging won't be possible and offer the legacy readline...

there's a piece of me that would like to get this out the door to have customers try in (in Preview) and see where we can improve.

[TylerLeonhardt]

It looks like this is by design:

PS C:\Users\tyleonha\Code\PowerShell\Misc> Set-PSBreakpoint -Line 3 -Script .\foo.ps1
Set-PSBreakpoint : Specified method is not supported.
At line:1 char:1
+ Set-PSBreakpoint -Line 3 -Script .\foo.ps1
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo          : NotImplemented: (:) [Set-PSBreakpoint], PSNotSupportedException
+ FullyQualifiedErrorId : NotSupported,Microsoft.PowerShell.Commands.SetPSBreakpointCommand

[SeeminglyScience]

Awesome! 🙂 what a wild ride that was eh?

[TylerLeonhardt]

Here is an overview of what got changed by this pull request:

Complexity increasing per file
==============================
- src/PowerShellEditorServices/Services/PowerShellContext/PowerShellContextService.cs  2
         

See the complete overview on Codacy

[SeeminglyScience]

LGTM!