android: Forward suspended() and resumed() events and patch up platform-specific documentation (#3786)

Key them off of `onStop()` and `onStart()` which seems to match the
other backends most closely.  These [Android Activity lifecycle] events
denote when the application is visible on-screen, and recommend that any
heavy lifting for startup and shutdown happens here, as the application
may be demoted to the background and later shut down entirely unless the
user navigates back to it.

[Android Activity lifecycle]: https://developer.android.com/guide/components/activities/activity-lifecycle

src/platform_impl/apple/appkit/window_delegate.rs

@@ -218,10 +218,10 @@ declare_class!(
             trace_scope!("windowDidResignKey:");
             // It happens rather often, e.g. when the user is Cmd+Tabbing, that the
             // NSWindowDelegate will receive a didResignKey event despite no event
-            // being received when the modifiers are released.  This is because
+            // being received when the modifiers are released. This is because
             // flagsChanged events are received by the NSView instead of the
             // NSWindowDelegate, and as a result a tracked modifiers state can quite
-            // easily fall out of synchrony with reality.  This requires us to emit
+            // easily fall out of synchrony with reality. This requires us to emit
             // a synthetic ModifiersChanged event when we lose focus.
             self.view().reset_modifiers();