MaterialDesignDataGridTextColumnPopupEditingStyle: Mouse and focus issues

When you double click on a cell which has EditingElementStyle="{StaticResource MaterialDesignDataGridTextColumnPopupEditingStyle}" defined, the popup appears but there are a few issues:

1. You can't move the cursor using the mouse and can't select text with the mouse (although right clicking brings up the context menu correctly).
2. If the cell editing popup is open and you change focus to another app, the popup remains on top of the other application.
3. (Minor/opinion) The cursor's position is at the beginning of the TextBox when the popup editor opens (I think this would typically be at the end?)

To reproduce:

• Open the WPF demo
• Selecting the "Grids" page using the menu
• Double click on a cell in the Name or Description columns to start editing
• Try using the left mouse button to move the cursor or select text inside the popup
• Switch to another application while the cell editor is open

Here's a screenshot of the popup over another window.

WPF デモの Grids ページと、Name 列および Description 列で使用されている MaterialDesignDataGridTextColumnPopupEditingStyle から始めます。ダブルクリックでポップアップの動作を再現し、その後、ポップアップエディターにおけるマウス選択、アプリケーションフォーカス、初期カーソル位置の処理を追跡します。完了条件は、マウスによる編集が機能し、ポップアップが別のアプリケーションの上に残り続けず、カーソルの動作に対処できていることです。