Update extension icon (and use a special preview icon) (#3493)

This aligns us with the icons used for PowerShell 7 and sufficiently
differentiates the PowerShell, PowerShell Preview, and Azure PowerShell
extensions on the marketplace.

Author: andyleejordan

media/PowerShell_Icon.png

@@ -16,7 +16,7 @@
     "Snippets",
     "Linters"
   ],
-  "icon": "media/PowerShell_icon.png",
+  "icon": "media/PowerShell_Icon.png",
   "galleryBanner": {
     "color": "#ACD1EC",
     "theme": "light"

media/PowerShell_Preview_Icon.png

@@ -327,11 +327,13 @@ function Update-Version {
                     $displayName = "PowerShell Preview"
                     $preview = "true"
                     $description = "(Preview) $d"
+                    $icon = "media/PowerShell_Preview_Icon.png"
                 } else {
                     $name = "powershell"
                     $displayName = "PowerShell"
                     $preview = "false"
                     $description = $d
+                    $icon = "media/PowerShell_Icon.png"
                 }
 
                 $path = "package.json"
@@ -343,6 +345,7 @@ function Update-Version {
                 $f = $f -replace '^(?<prefix>  "version":\s+")(.+)(?<suffix>",)$', "`${prefix}${v}`${suffix}"
                 $f = $f -replace '^(?<prefix>  "preview":\s+)(.+)(?<suffix>,)$', "`${prefix}${preview}`${suffix}"
                 $f = $f -replace '^(?<prefix>  "description":\s+")(.+)(?<suffix>",)$', "`${prefix}${description}`${suffix}"
+                $f = $f -replace '^(?<prefix>  "icon":\s+")(.+)(?<suffix>",)$', "`${prefix}${icon}`${suffix}"
                 $f | Set-Content -Path $path
                 git add $path
             }

media/PowerShell_icon.png

@@ -60,7 +60,7 @@ function NewReleaseVersionEntry
             }
             [ordered]@{
                 assetType = 'Microsoft.VisualStudio.Services.Icons.Default'
-                source = 'https://raw.githubusercontent.com/PowerShell/vscode-powershell/master/media/PowerShell_icon.png'
+                source = 'https://raw.githubusercontent.com/PowerShell/vscode-powershell/master/media/PowerShell_Icon.png'
             }
             [ordered]@{
                 assetType = 'Microsoft.VisualStudio.Services.Content.Details'