Add external API part 1

[TylerLeonhardt]

PR Summary

This adds the foundation of the API that external extensions will use. Once @rjmholt is done with the work in PSES to better handle the runspace, we can add part 2 which will execute PowerShell script in the PowerShell runspace.

Here are the messages that are encompassed in this PR:

RegisterExternalExtension

I want to be able to track what extensions are leveraging this feature.
In order to do this,
we can have them register first.
With that,
they'll get a UUID back that they use in any future request.
It's like an API KEY of sorts...

vscode.commands.executeCommand(
    "PowerShell.RegisterExternalExtension",
    "ms-vscode.PesterTestExplorer" // the name of the extension using us
    "v1"); // API Version. I made it a single number because I don't want to be in the business of maintaining 1.x.x versions
// returns string session uuid

UnregisterExternalExtension

This will remove the session. Not a very useful API, but it's there.

vscode.commands.executeCommand(
    "PowerShell.UnregisterExternalExtension",
    "uuid"); // the uuid from above for tracking purposes
// returns boolean

GetPowerShellVersionDetails

This will fetch the version details of the PowerShell used to start VS Code.

vscode.commands.executeCommand(
    "PowerShell.GetPowerShellVersionDetails",
    "uuid"); // the uuid from above for tracking purposes

This will return an object with common properties that might be useful:

{
    exePath: "/usr/local/bin/pwsh",
    verison: "7.1.0-preview.4",
    displayName: "PowerShell Preview (x64)", // comes from the Session Menu
    architecture: "x64"
}

PR Checklist

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• PR has tests
• 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

[rjmholt]

Really like the tests

[rjmholt]

Is there a log.writeError -- should we use that if we're throwing?

[TylerLeonhardt]

My thinking was that the logs are really for us, not the extension author. To help the extension author a bit, I used warning... but technically it's user error, not our issue. So I felt it didn't deserve writeError. But happy to change it. I don't care too much.

[rjmholt]

Given that this object sets its fields in the constructor, it might be nicer if each command were a method on the class (and then the comments describing them could be on those methods maybe), and then have the commands array just point to those

[TylerLeonhardt]

I like that

[TylerLeonhardt]

changed.

[TylerLeonhardt]

btw this message will allow me to delete this file :) in the test explorer code

https://github.com/TylerLeonhardt/vscode-powershell-test-adapter/blob/master/src/process.ts

[TylerLeonhardt]

ok merge time