Support macOS-style Switch about flutter HOT 1 OPEN

mixin _SwitchConfig {
  double get trackHeight;
  double get trackWidth;
  double get thumbRadius;
  double get ThumbExtension; // This is 7 for iOS switch, 1 for macOS switch
}

class _SwitchConfigIOS with _SwitchConfig {
  ...
  @override
  double get ThumbExtension => 7.0;
}

class _SwitchConfigMacOS with _SwitchConfig {
  ...
  @override
  double get ThumbExtension => 1.0;
}

final _SwitchConfig config = switch (platform) {
  TargetPlatform.android || TargetPlatform.fuchsia || TargetPlatform.iOS => _SwitchConfigIOS(context),
  TargetPlatform.linux || TargetPlatform.windows || TargetPlatform.macOS => _SwitchConfigMacOS(context),
}