Change the value of kMaxUnsignedSMI for the Web (#37266)

* Sync the value kMaxUnsignedSMI for the Web

* update events.dart docs

packages/flutter/lib/src/foundation/_bitfield_web.dart

@@ -5,7 +5,13 @@
 import 'bitfield.dart' as bitfield;
 
 /// The dart:html implementation of [bitfield.kMaxUnsignedSMI].
-const int kMaxUnsignedSMI = 0;
+///
+/// This value is used as an optimization to coerse some numbers to be within
+/// the SMI range and avoid heap allocations. Because number encoding is
+/// VM-specific, there's no guarantee that this optimization will be effective
+/// on all JavaScript engines. The value picked here should be correct, but it
+/// does not have to guarantee efficiency.
+const int kMaxUnsignedSMI = -1;
 
 /// The dart:html implementation of [bitfield.Bitfield].
 class BitField<T extends dynamic> implements bitfield.BitField<T> {

packages/flutter/lib/src/gestures/events.dart

@@ -116,7 +116,8 @@ const int kTouchContact = kPrimaryButton;
 
 /// The bit of [PointerEvent.buttons] that corresponds to the nth mouse button.
 ///
-/// The `number` argument can be at most 62.
+/// The `number` argument can be at most 62 in Flutter for mobile and desktop,
+/// and at most 32 on Flutter for web.
 ///
 /// See [kPrimaryMouseButton], [kSecondaryMouseButton], [kMiddleMouseButton],
 /// [kBackMouseButton], and [kForwardMouseButton] for semantic names for some
@@ -125,7 +126,8 @@ int nthMouseButton(int number) => (kPrimaryMouseButton << (number - 1)) & kMaxUn
 
 /// The bit of [PointerEvent.buttons] that corresponds to the nth stylus button.
 ///
-/// The `number` argument can be at most 62.
+/// The `number` argument can be at most 62 in Flutter for mobile and desktop,
+/// and at most 32 on Flutter for web.
 ///
 /// See [kPrimaryStylusButton] and [kSecondaryStylusButton] for semantic names
 /// for some stylus buttons.