Add support for MotionEvent pointer history

This exposes `MotionEvent` pointer history via a `PointerHistoryIter`, got via
`Pointer::history()`, that yields `HistoricPointer`'s that give access to
sub-sample timestamps and axis values between events.

This adds consistent pointer history support for both the `native-activity` and
`game-activity` backends.

For example, historical pointer samples can be iterated like:

```rust
let num_pointers = motion_event.pointer_count();
for i in 0..num_pointers {
    let pointer = motion_event.pointer_at_index(i);
    println!(
        "Pointer[{i}]: id={}, time={}, x={}, y={}",
        pointer.pointer_id(),
        motion_event.event_time(),
        pointer.x(),
        pointer.y(),
    );
    for sample in pointer.history() {
        println!(
            "  History[{}]: x={}, y={}, time={:?}",
            sample.history_index(),
            sample.x(),
            sample.y(),
            sample.event_time()
        );
    }
}
```

The documentation clarifies that each pointer will have the same number of
historic samples, and the timestamps for corresponding samples will match.

The `PointerHistoryIter` supports forwards and/or backwards iteration and can
be queried for its `.len()`.

Fixes: #207

Author: rib

android-activity/CHANGELOG.md

@@ -50,6 +50,9 @@ fn android_on_create(state: &OnCreateState) {
 }
 ```
 
+- Support for `MotionEvent` history, providing higher fidelity input data for things like stylus input (`native-activity` + `game-activity` backends). ([#218](https://github.com/rust-mobile/android-activity/pull/218))
+
+
 ### Changed
 
 - rust-version bumped to 1.85.0 ([#193](https://github.com/rust-mobile/android-activity/pull/193), [#219](https://github.com/rust-mobile/android-activity/pull/219))