Fix "Create New" script to open the script file after creation (#499)

When using the "Create New" functionality to create a Python script, the
script file was being created successfully but not opened in the editor,
requiring users to manually navigate and open the file.

This PR fixes the issue by modifying the `addPythonProjectCommand`
function to:

1. Capture the return value from `creator.create()`
2. Check if the result is a `Uri` (indicating a single file like a
script was created)
3. Call `showTextDocument(uri)` to automatically open the script in the
editor

**Before:**
- User selects "Create New" → Script → enters name
- Script file is created but user has to manually find and open it

**After:**
- User selects "Create New" → Script → enters name  
- Script file is created AND automatically opened in the editor

The implementation is minimal and surgical:
- Only affects cases where creators return a `Uri` (like script files)
- Projects that return `PythonProject` objects are unaffected
- Uses existing `showTextDocument` utility function
- Applied to both the main creator path and existing projects creator
path

Fixes #478.

---

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---------

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: eleanorjboyd <[email protected]>

Author: Copilot

src/features/envCommands.ts

@@ -27,7 +27,7 @@ import {
     pickWorkspaceFolder,
 } from '../common/pickers/managers';
 import { pickProject, pickProjectMany } from '../common/pickers/projects';
-import { activeTextEditor, showErrorMessage, showInformationMessage } from '../common/window.apis';
+import { activeTextEditor, showErrorMessage, showInformationMessage, showTextDocument } from '../common/window.apis';
 import { quoteArgs } from './execution/execUtils';
 import { runAsTask } from './execution/runAsTask';
 import { runInTerminal } from './terminal/runInTerminal';
@@ -471,7 +471,10 @@ export async function addPythonProjectCommand(
     }
 
     try {
-        await creator.create(options);
+        const result = await creator.create(options);
+        if (result instanceof Uri) {
+            await showTextDocument(result);
+        }
     } catch (ex) {
         if (ex === QuickInputButtons.Back) {
             return addPythonProjectCommand(resource, wm, em, pc);