PS: Fix the top level arguments after the AST cleanup.

Author: MathiasVP

powershell/ql/lib/semmle/code/powershell/ast/internal/FunctionBase.qll

@@ -21,3 +21,8 @@ class FunctionBase extends Ast, TFunctionBase {
 
   final int getNumberOfParameters() { result = count(this.getAParameter()) }
 }
+
+/**
+ * The implicit function that represents the entire script block in a file.
+ */
+class TopLevelFunction extends FunctionBase, TTopLevelFunction { }

powershell/ql/lib/semmle/code/powershell/dataflow/flowsources/Local.qll

@@ -59,7 +59,7 @@ private class ExternalCommandLineArgumentSource extends CommandLineArgumentSourc
  * A data flow source that represents the parameters of the `Main` method of a program.
  */
 private class MainMethodArgumentSource extends CommandLineArgumentSource {
-  MainMethodArgumentSource() { this.asParameter().getParent() instanceof TopLevelScriptBlock }
+  MainMethodArgumentSource() { this.asParameter().getFunction() instanceof TopLevelFunction }
 }
 
 /**