Introduce CursorType and add it to CursorMoved::type

- This adds pen/stylus support.
- Move `Force::Calibrated::altitude_angle` to `ToolAngle::altitude`.
- `Force::normalized()` now takes a `Option<ToolAngle>` to calculate the perpendicular force.
- Just introducing types, no implementation yet!

docs/res/ATTRIBUTION.md

@@ -9,3 +9,10 @@ by [Tomiĉo] (https://commons.wikimedia.org/wiki/User:Tomi%C4%89o). It was
 originally released under the [CC-BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0/deed.en)
 License. Minor modifications have been made by [John Nunley](https://github.com/notgull),
 which have been released under the same license as a derivative work.
+
+## tool_*.webp
+
+These files are converted versions of
+[W3C Pointer Events spec images](https://github.com/w3c/pointerevents/tree/93938ae7fe0172e2ae7587ad7d7c4fc8562d7153/images)
+by [patrickhlauke](https://github.com/patrickhlauke). It is licensed under the
+[W3C Software and Document License](https://www.w3.org/copyright/software-license).

src/changelog/unreleased.md

@@ -44,6 +44,7 @@ changelog entry.
 
 - Add `ActiveEventLoop::create_proxy()`.
 - On Web, implement `Error` for `platform::web::CustomCursorError`.
+- Add `CursorMoved::type` with a new type `CursorType` introducing pen/stylus support.
 
 ### Changed
 
@@ -70,6 +71,7 @@ changelog entry.
 - Change signature of `EventLoop::run_app`, `EventLoopExtPumpEvents::pump_app_events` and
   `EventLoopExtRunOnDemand::run_app_on_demand` to accept a `impl ApplicationHandler` directly,
   instead of requiring a `&mut` reference to it.
+- `Force::normalized()` now takes a `Option<ToolAngle>` to calculate the perpendicular force.
 
 ### Removed
 
@@ -82,6 +84,7 @@ changelog entry.
   This feature was incomplete, and the equivalent functionality can be trivially achieved outside
   of `winit` using `objc2-ui-kit` and calling `UIDevice::currentDevice().userInterfaceIdiom()`.
 - On Web, remove unused `platform::web::CustomCursorError::Animation`.
+- Remove `Force::Calibrated::altitude_angle` in favor of `ToolAngle::altitude`.
 
 ### Fixed