Redesign the Command Explorer around modules and lazy loading

The Command Explorer fetched the full command table up front (names, modules,
and parameter metadata for everything), which took minutes to populate and
showed a flat, hard-to-scan list. Rework it into a lazy, module-grouped tree:

- Top-level nodes are modules (with version), expanded on demand; their
  commands are fetched per module with `excludeParameters` so only names and
  modules cross the wire.
- Module-less commands are collected under a neutral "Functions & Scripts"
  node with a folder icon, and the request sets `excludeDefaultFunctions` so
  PowerShell's default-session plumbing doesn't clutter it.
- Hovering a module shows its metadata via the new `powerShell/getModule`
  request, cached so repeated hovers don't re-fetch.
- The inline Show Help / Insert command actions are gated to `viewItem ==
  command` so they no longer appear on module nodes.

Default the Command Explorer to visible. Because its default now equals the
value the ISE profile sets, the ISE compatibility tests could no longer
observe a revert by inequality; guard those assertions with
`revertIsObservable`, which skips settings whose default already matches the
ISE value.

Drafted by Copilot (Claude Opus 4.8).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: andyleejordan

package.json

@@ -210,7 +210,7 @@
         "command": "PowerShell.InsertCommand",
         "title": "Insert Command",
         "category": "PowerShell",
-        "icon": "$(pencil)"
+        "icon": "$(arrow-right)"
       },
       {
         "command": "PowerShell.ShowHelp",
@@ -398,12 +398,12 @@
       "view/item/context": [
         {
           "command": "PowerShell.ShowHelp",
-          "when": "view == PowerShellCommands",
+          "when": "view == PowerShellCommands && viewItem == command",
           "group": "inline@1"
         },
         {
           "command": "PowerShell.InsertCommand",
-          "when": "view == PowerShellCommands",
+          "when": "view == PowerShellCommands && viewItem == command",
           "group": "inline@2"
         }
       ]
@@ -755,7 +755,7 @@
           },
           "powershell.sideBar.CommandExplorerVisibility": {
             "type": "boolean",
-            "default": false,
+            "default": true,
             "markdownDescription": "Specifies the visibility of the Command Explorer in the side bar."
           },
           "powershell.sideBar.CommandExplorerExcludeFilter": {