use sentence case in error message titles (#35750)

* use sentence case in error message titles

* add a test

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

@@ -459,7 +459,7 @@ class FlutterErrorDetails extends Diagnosticable {
 
   @override
   String toStringShort() {
-    return library != null ? 'Exception Caught By $library' : 'Exception Caught';
+    return library != null ? 'Exception caught by $library' : 'Exception caught';
   }
 
   @override

packages/flutter/test/foundation/assertions_test.dart

@@ -122,6 +122,20 @@ void main() {
     );
   });
 
+  test('FlutterErrorDetails.toStringShort', () {
+    expect(
+        FlutterErrorDetails(
+          exception: 'MESSAGE',
+          library: 'library',
+          context: ErrorDescription('CONTEXTING'),
+          informationCollector: () sync* {
+            yield ErrorDescription('INFO');
+          },
+        ).toStringShort(),
+        'Exception caught by library',
+    );
+  });
+
   test('FlutterError default constructor', () {
     FlutterError error = FlutterError(
       'My Error Summary.\n'