Rust: Don't use macro in test and add documentation string

Author: paldepind

rust/ql/lib/codeql/rust/controlflow/internal/Scope.qll

@@ -4,8 +4,10 @@ private import ControlFlowGraphImpl
 private import codeql.rust.internal.generated.ParentChild
 
 abstract class CfgScope extends AstNode {
+  /** Holds if `first` is executed first when entering scope. */
   abstract predicate scopeFirst(AstNode first);
 
+  /** Holds if scope is exited when `last` finishes with completion `c`. */
   abstract predicate scopeLast(AstNode last, Completion c);
 }