Add Stylus Eraser Button Support (S-Pen, Wacom, XP-Pen)

Yoloamigo

Currently, the PDF reader's eraser tool only works through manual toolbar selection. Users with stylus devices like S-Pen, Wacom, or XP-Pen need to click the toolbar button every time they want to erase, even though their stylus has a dedicated eraser button. I want the eraser button to work, pressing it automatically activating eraser mode without requiring toolbar interaction.