text [nfc]: Make weightVariableTextStyle's context param required

lib/widgets/content.dart

@@ -765,7 +765,7 @@ class _InlineContentBuilder {
   }
 
   InlineSpan _buildStrong(StrongNode node) => _buildNodes(node.nodes,
-    style: weightVariableTextStyle(_context, wght: 600, wghtIfPlatformRequestsBold: 900));
+    style: weightVariableTextStyle(_context!, wght: 600, wghtIfPlatformRequestsBold: 900));
 
   InlineSpan _buildDeleted(DeletedNode node) => _buildNodes(node.nodes,
     style: const TextStyle(decoration: TextDecoration.lineThrough));

lib/widgets/text.dart

@@ -203,13 +203,12 @@ const kButtonTextLetterSpacingProportion = 0.01;
 /// ```
 ///
 /// See also [FontVariation] for more background on variable fonts.
-// TODO(a11y) make `context` required when callers can adapt?
-TextStyle weightVariableTextStyle(BuildContext? context, {
+TextStyle weightVariableTextStyle(BuildContext context, {
   double? wght,
   double? wghtIfPlatformRequestsBold,
 }) {
   double value = wght ?? FontWeight.normal.value.toDouble();
-  if (context != null && MediaQuery.boldTextOf(context)) {
+  if (MediaQuery.boldTextOf(context)) {
     // The framework has a condition on [MediaQueryData.boldText]
     // in the [Text] widget, but that only affects `fontWeight`.
     // [Text] doesn't know where to land on the chosen font's "wght" axis if any,

test/widgets/text_test.dart

@@ -105,15 +105,6 @@ void main() {
       });
     }
 
-    testWeights('no context passed; default wght values',
-      styleBuilder: (context) => weightVariableTextStyle(null),
-      expectedFontVariations: const [FontVariation('wght', 400)],
-      expectedFontWeight: FontWeight.normal);
-    testWeights('no context passed; specific wght',
-      styleBuilder: (context) => weightVariableTextStyle(null, wght: 225, wghtIfPlatformRequestsBold: 425),
-      expectedFontVariations: const [FontVariation('wght', 225)],
-      expectedFontWeight: FontWeight.w200);
-
     testWeights('default values; platform does not request bold',
       styleBuilder: (context) => weightVariableTextStyle(context),
       platformRequestsBold: false,