🐛 Respect user choice when dismissing the powerShellExePath dialog

[bergmeister]

PR Summary

Currently the extension actually changes the user's powerShellExePath if the user dismisses the presented dialog by clicking on the x button.
The VS-Code API vscode.window.showWarningMessage(message: string, items: string[]) returns undefined when the user dismisses the dialog: https://code.visualstudio.com/api/references/vscode-api#window.showWarningMessage

PR Checklist

Note: Tick the boxes below that apply to this pull request by putting an x between the square brackets.
Please mark anything not applicable to this PR NA.

• PR has a meaningful title
• Summarized changes
• 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

[TylerLeonhardt]

Hmmm I feel like they changed the API... But LGTM

[bergmeister]

Hmmm I feel like they changed the API... But LGTM

I doubt it, their code hasn't changed since they added it 3 years ago here (comments are still the same) and I even looked 2 layers down to when it calls extHostMessageService.showMessage.