Update all `package.json` descriptions

### Prerequisites

- [X] I have written a descriptive issue title.
- [X] I have searched all [issues](https://.com/PowerShell/vscode-powershell/issues?q=is%3Aissue) to ensure it has not already been reported.

### Summary

Quite a few of our setting and command descriptions in `package.json`, for instance:

```
        "powershell.scriptAnalysis.enable": {
          "type": "boolean",
          "default": true,
          "description": "Enables real-time script analysis from PowerShell Script Analyzer. Uses the newest installed version of the PSScriptAnalyzer module or the version bundled with this extension, if it is newer."
        },
```

is totally wrong.

I was about to fix just this, but then was looking through and _most_ if not all of these should be reviewed and updated. Furthermore, it would be a great improvement to switch to `markdownDescription` and have proper links to mentioned settings, etc.

### Proposed Design

_No response_