[rfw] Fix fontWeight not applied in release mode

FontWeight is not a real Dart enum; it is a hand-crafted class with
static const members. The previous implementation decoded fontWeight via
enumValue(), which matched strings against FontWeight.value.toString().
In AOT/release builds this is not guaranteed to be stable, so matches
silently failed and fontWeight defaulted to null (rendered as w400).

Add a dedicated ArgumentDecoders.fontWeight() method that maps strings
("w100"–"w900", "normal", "bold") and integers (100–900) to the correct
FontWeight constant using an explicit switch, without relying on
toString(). Update textStyle and strutStyle to use it.

Fixes flutter/flutter#180223

Made-with: Cursor

Author: iam-abhijha

packages/rfw/lib/src/flutter/argument_decoders.dart

@@ -632,6 +632,46 @@ class ArgumentDecoders {
     return null;
   }
 
+  /// Returns a [FontWeight] from the specified string or integer.
+  ///
+  /// This does not use [FontWeight.toString], which is not guaranteed to be
+  /// stable in release builds (since [FontWeight] is not a real Dart enum).
+  ///
+  /// Supported string values: `"w100"` through `"w900"`, `"normal"` (mapped to
+  /// [FontWeight.w400]), and `"bold"` (mapped to [FontWeight.w700]).
+  ///
+  /// Supported integer values: `100` through `900` in increments of 100.
+  static FontWeight? fontWeight(DataSource source, List<Object> key) {
+    final int? numeric = source.v<int>(key);
+    if (numeric != null) {
+      switch (numeric) {
+        case 100: return FontWeight.w100;
+        case 200: return FontWeight.w200;
+        case 300: return FontWeight.w300;
+        case 400: return FontWeight.w400;
+        case 500: return FontWeight.w500;
+        case 600: return FontWeight.w600;
+        case 700: return FontWeight.w700;
+        case 800: return FontWeight.w800;
+        case 900: return FontWeight.w900;
+      }
+    }
+    switch (source.v<String>(key)) {
+      case 'w100': return FontWeight.w100;
+      case 'w200': return FontWeight.w200;
+      case 'w300': return FontWeight.w300;
+      case 'w400':
+      case 'normal': return FontWeight.w400;
+      case 'w500': return FontWeight.w500;
+      case 'w600': return FontWeight.w600;
+      case 'w700':
+      case 'bold': return FontWeight.w700;
+      case 'w800': return FontWeight.w800;
+      case 'w900': return FontWeight.w900;
+    }
+    return null;
+  }
+
   /// Returns a [FontFeature] from the specified map.
   ///
   /// The `feature` key is used as the font feature name (defaulting to the
@@ -1276,7 +1316,7 @@ class ArgumentDecoders {
   /// following keys: 'fontFamily` (string), `fontFamilyFallback` ([list] of
   /// [string]), `fontSize` (double), `height` (double), `leadingDistribution`
   /// ([enumValue] of [TextLeadingDistribution]), `leading` (double),
-  /// `fontWeight` ([enumValue] of [FontWeight]), `fontStyle` ([enumValue] of
+  /// `fontWeight` ([fontWeight]), `fontStyle` ([enumValue] of
   /// [FontStyle]), `forceStrutHeight` (boolean).
   static StrutStyle? strutStyle(DataSource source, List<Object> key) {
     if (!source.isMap(key)) {
@@ -1289,7 +1329,7 @@ class ArgumentDecoders {
       height: source.v<double>([...key, 'height']),
       leadingDistribution: enumValue<TextLeadingDistribution>(TextLeadingDistribution.values, source, [...key, 'leadingDistribution']),
       leading: source.v<double>([...key, 'leading']),
-      fontWeight: enumValue<FontWeight>(FontWeight.values, source, [...key, 'fontWeight']),
+      fontWeight: fontWeight(source, [...key, 'fontWeight']),
       fontStyle: enumValue<FontStyle>(FontStyle.values, source, [...key, 'fontStyle']),
       forceStrutHeight: source.v<bool>([...key, 'forceStrutHeight']),
     );
@@ -1350,7 +1390,7 @@ class ArgumentDecoders {
   ///
   /// Otherwise (even if it has no keys), the [TextStyle] is created from the
   /// following keys: `color` ([color]), `backgroundColor` ([color]), `fontSize`
-  /// (double), `fontWeight` ([enumValue] of [FontWeight]), `fontStyle`
+  /// (double), `fontWeight` ([fontWeight]), `fontStyle`
   /// ([enumValue] of [FontStyle]), `letterSpacing` (double), `wordSpacing`
   /// (double), `textBaseline` ([enumValue] of [TextBaseline]), `height`
   /// (double), `leadingDistribution` ([enumValue] of
@@ -1369,7 +1409,7 @@ class ArgumentDecoders {
       color: color(source, [...key, 'color']),
       backgroundColor: color(source, [...key, 'backgroundColor']),
       fontSize: source.v<double>([...key, 'fontSize']),
-      fontWeight: enumValue<FontWeight>(FontWeight.values, source, [...key, 'fontWeight']),
+      fontWeight: fontWeight(source, [...key, 'fontWeight']),
       fontStyle: enumValue<FontStyle>(FontStyle.values, source, [...key, 'fontStyle']),
       letterSpacing: source.v<double>([...key, 'letterSpacing']),
       wordSpacing: source.v<double>([...key, 'wordSpacing']),

packages/rfw/test/argument_decoders_test.dart

@@ -187,6 +187,19 @@ void main() {
     await tester.pump();
     expect(tester.widget<Directionality>(find.byType(Directionality)).textDirection, TextDirection.ltr);
 
+    runtime.update(const LibraryName(<String>['test']), parseLibraryFile('''
+      import core;
+      widget root = Directionality(
+        textDirection: "ltr",
+        child: Text(
+          text: 'Hello',
+          style: { fontWeight: "w700" },
+        ),
+      );
+    '''));
+    await tester.pump();
+    expect(tester.widget<Text>(find.byType(Text)).style!.fontWeight, FontWeight.w700);
+
     runtime.update(const LibraryName(<String>['test']), parseLibraryFile('''
       import core;
       widget root = FittedBox(