Modify powerShellDefaultVersion desc to make clearer

Update session menu "switch to" entries to more clearly distinguish the
"version name".

Fix #1734

Author: rkeithhill

package.json

@@ -543,7 +543,7 @@
         },
         "powershell.powerShellDefaultVersion": {
           "type": "string",
-          "description": "Specifies the name of the PowerShell version used in the startup session when the extension loads e.g \"Windows PowerShell (x86)\" or \"PowerShell Core 6.0.2 (x64)\"."
+          "description": "Specifies the PowerShell version name, as displayed by the 'PowerShell: Show Session Menu' command, used when the extension loads e.g \"Windows PowerShell (x86)\" or \"PowerShell Core 6 (x64)\"."
         },
         "powershell.startAutomatically": {
           "type": "boolean",

src/session.ts

@@ -761,7 +761,7 @@ export class SessionManager implements Middleware {
                 .filter((item) => item.exePath.toLowerCase() !== currentExePath)
                 .map((item) => {
                     return new SessionMenuItem(
-                        `Switch to ${item.versionName}`,
+                        `Switch to: ${item.versionName}`,
                         () => { this.changePowerShellExePath(item.exePath); });
                 });