The confirmation message is inconsistent when deleting a resource group from context menu and command palette

[v-xinda]

OS: Win10
Azure Resource Extension Build Version: 20220609.5
Regression: Not a regression

Repro Steps:

1. Right click a resource group -> Click "Delete Resource Group..." -> Check the confirmation message in the dialog.
2. F1 -> Click "Azure: Delete Resource Group..." -> Select the above selected resource group -> Check the confirmation message in the dialog.
3. Check whether the confirmation message is consistent between in the step1 and step 2.

Expect:
The confirmation message is consistent between in the step1 and step 2.

Actual:
The confirmation message is inconsistent between in the step1 and step 2.

[alexweininger]

Since this number is derived from the cached children, there are a few other cases where it breaks. For example, we're counting this UI-only tree item as a resource.