Allow deletion of only item in AST (#6335)

* Update test to check for deletion of only operation

* Allow updateEditorWithAstAndWriteToFile to clear AST

* Update src/lang/codeManager.ts

Co-authored-by: Jonathan Tran <jonnytran@gmail.com>

* Weave `isDeleting` through to `deleteSelectionPromise`

* fmt

---------

Co-authored-by: Jonathan Tran <jonnytran@gmail.com>
Co-authored-by: Pierre Jacquier <pierrejacquier39@gmail.com>

e2e/playwright/feature-tree-pane.spec.ts

@@ -430,5 +430,17 @@ profile003 = startProfileAt([0, -4.93], sketch001)
       await editor.expectEditor.not.toContain('sketch001 =')
       await editor.expectEditor.not.toContain('profile002 = ')
     })
+
+    await test.step(`Delete the remaining plane via feature tree`, async () => {
+      const operationButton = await toolbar.getFeatureTreeOperation(
+        'Offset Plane',
+        0
+      )
+      await operationButton.click({ button: 'left' })
+      await page.keyboard.press('Delete')
+
+      // Verify the plane code is gone, and https://github.com/KittyCAD/modeling-app/issues/5988 is fixed.
+      await editor.expectEditor.not.toContain('plane001 =')
+    })
   })
 })