C#: Add extractor error test for global statement extraction

Author: tamasvajk

csharp/ql/test/library-tests/csharp9-standalone/ExtractorError.expected

@@ -0,0 +1 @@
+| GlobalStmt.cs:13:6:13:6 | TagStack unexpectedly empty | Unexpected C# extractor error: TagStack unexpectedly empty\n |

csharp/ql/test/library-tests/csharp9-standalone/ExtractorError.ql

@@ -0,0 +1,7 @@
+import csharp
+import semmle.code.csharp.commons.Diagnostics
+
+from ExtractorError error
+where not exists(CompilerError ce | ce.getLocation().getFile() = error.getLocation().getFile())
+select error,
+  "Unexpected " + error.getOrigin() + " error: " + error.getText() + "\n" + error.getStackTrace()