Add semantics constants to the exported symbols list for the embedder library

shell/platform/embedder/embedder_exports.lst

@@ -8,6 +8,7 @@
   global:
     Flutter*;
     __Flutter*;
+    kFlutter*;
     kDartIsolateSnapshotData;
     kDartIsolateSnapshotInstructions;
     kDartVmSnapshotData;

testing/symbols/verify_exported.dart

@@ -274,7 +274,8 @@ int _checkLinux(String outPath, String nmPath, Iterable<String> builds) {
         break;
       }
       if (!(entry.name.startsWith('Flutter')
-            || entry.name.startsWith('__Flutter'))) {
+            || entry.name.startsWith('__Flutter')
+            || entry.name.startsWith('kFlutter'))) {
         print('ERROR: $libFlutter exports an unexpected symbol name: ($entry)');
         print(' Library has $entries.');
         failures++;