Windows Tablet interacts strangely with UI

[Fuzzyzilla]

Two bugs have been spotted with the octotablet-egui integration implemented in window.rs and stylus_events.rs (thanks marco~!)

• When "Display Scale" (dpi) is not 100%, the stylus location is scaled incorrectly. With scales above 100%, the interactive region is squished towards the top left. This does not effect stylus interaction with the document, and does not affect the mouse.
• Stylus events are double-counted, presumably windows emulates mouse motion when the stylus moves (unrelated to the emulate_tool_from_mouse option in octotablet which controls the reverse). This causes jagged stroke previews and mis-counted clicks on UI elements.