changelog: add device pointer button to pointer overhaul entry

Author: elytldr

winit/src/changelog/unreleased.md

@@ -168,7 +168,9 @@ changelog entry.
     type to a generic mouse button.
   - New `FingerId` added to `PointerKind::Touch` and `PointerSource::Touch` able to uniquely
     identify a finger in a multi-touch interaction. Replaces the old `Touch::id`.
-  - In the same spirit rename `DeviceEvent::MouseMotion` to `PointerMotion`.
+  - In the same spirit rename `DeviceEvent::MouseMotion` and `DeviceEvent::Button` to
+    `PointerMotion` and `PointerButton` respectively.
+  - Change `DeviceEvent::PointerButton` to use `ButtonSource`.
   - Remove `Force::Calibrated::altitude_angle`.
 - On X11, use bottom-right corner for IME hotspot in `Window::set_ime_cursor_area`.
 - On macOS and iOS, no longer emit `ScaleFactorChanged` upon window creation.