[material_ui] SnackBarThemeData.lerp drops showCloseIcon #195390

Steps to reproduce

const a = SnackBarThemeData(showCloseIcon: true);
final lerped = SnackBarThemeData.lerp(a, a.copyWith(elevation: 4), 0.5);
print(lerped.showCloseIcon); // null

Expected results

showCloseIcon is true, like every other non-lerpable field in SnackBarThemeData.lerp (such as behavior and dismissDirection), which take a's value below t = 0.5 and b's value above it.

Actual results

showCloseIcon is always null, because SnackBarThemeData.lerp never passes it to the constructor.

ThemeData.lerp calls this method, so during an AnimatedTheme transition, such as switching between light and dark mode, a snack bar shown mid-animation loses the close icon its theme asked for.

Package version

material_ui 1.8.0 (main as of today)