Fix value computation for multi-line strings (issue 22993)

pkg/analyzer/test/generated/parser_test.dart

Index: pkg/analyzer/test/generated/parser_test.dart
diff --git a/pkg/analyzer/test/generated/parser_test.dart b/pkg/analyzer/test/generated/parser_test.dart
index 648ea6bfa913931cbcdf119ebd4e015801ca4fba..6e0e5f9f9382daa1103da09afe989bf112fa1e71 100644
--- a/pkg/analyzer/test/generated/parser_test.dart
+++ b/pkg/analyzer/test/generated/parser_test.dart
@@ -8834,6 +8834,18 @@ void''');
     expect(elements[4] is InterpolationString, isTrue);
   }
 
+  void test_parseStringLiteral_multiline_trimmed() {
+    SimpleStringLiteral literal = parse4("parseStringLiteral", "''' \\\na'''");
+    expect(literal.literal, isNotNull);
+    expect(literal.value, "a");
+  }
+
+  void test_parseStringLiteral_multiline_untrimmed() {
+    SimpleStringLiteral literal = parse4("parseStringLiteral", "''' a\nb'''");
+    expect(literal.literal, isNotNull);
+    expect(literal.value, " a\nb");
+  }
+
   void test_parseStringLiteral_single() {
     SimpleStringLiteral literal = parse4("parseStringLiteral", "'a'");
     expect(literal.literal, isNotNull);