Provide checkbox option to use PSReadline beta version

[thegraffix]

Prerequisites

• I have written a descriptive issue title.
• I have searched all issues to ensure it has not already been reported.

Summary

The option to choose between stable and beta releases of PSReadline would be helpful.

Proposed Design

• Install both the latest stable and beta versions of the PSReadline module side by side.
• Add a checkbox in the VSCode options:
  [√] Use PSReadline beta version (default value of "checked")

[JustinGrote]

This would probably end up being a bug farm, but as a workaround, you can run Open Extensions Folder in the command palette, then go to ms-vscode.powershell/modules folder and remove and replace the PSReadline that is there. Should work fine, though you'll probably also want to pin your extension version and update manually after each update.

I'm going to flag it as Up for Grabs, but any setting needs to come with a very clear disclaimer. We also aren't going to ship beta psreadline in the extension as that is unnecessary bloat (though we do ship betas in the module on occasion as the primary version) so the implementation would need to find the psreadline beta or otherwise specify its path manually.

[thegraffix]

In fact that's exactly what I'm doing right now, replacing the existing PSReadline 2.4.0 folder with the latest stable version (2.3.6 right now). Initially, I was a bit confused as to why a PSReadline beta was included to begin with -- so thank you for the explanation 🙂 All of that makes perfect sense.

[andyleejordan]

@SydneyhSmith can you expand on the reason we included the beta for the last few releases? I noticed there have been a few stable releases since, though of the 2.3 series, not 2.4. What were we gaining with 2.4?