Swift: add comments about SwiftDispatcher lifetime

swift/extractor/visitors/DeclVisitor.h

@@ -7,6 +7,7 @@ namespace codeql {
 
 class DeclVisitor : public swift::DeclVisitor<DeclVisitor> {
  public:
+  // SwiftDispatcher should outlive the DeclVisitor
   DeclVisitor(SwiftDispatcher& dispatcher) : dispatcher(dispatcher) {}
 
   template <typename E>

swift/extractor/visitors/ExprVisitor.h

@@ -7,6 +7,7 @@ namespace codeql {
 
 class ExprVisitor : public swift::ExprVisitor<ExprVisitor> {
  public:
+  // SwiftDispatcher should outlive the ExprVisitor
   ExprVisitor(SwiftDispatcher& dispatcher) : dispatcher(dispatcher) {}
 
   template <typename E>

swift/extractor/visitors/PatternVisitor.h

@@ -20,6 +20,7 @@ class PatchedPatternVisitor : public swift::PatternVisitor<ImplClass, PatternRet
 
 class PatternVisitor : public PatchedPatternVisitor<PatternVisitor> {
  public:
+  // SwiftDispatcher should outlive the PatternVisitor
   PatternVisitor(SwiftDispatcher& dispatcher) : dispatcher(dispatcher) {}
 
   template <typename E>

swift/extractor/visitors/StmtVisitor.h

@@ -21,6 +21,7 @@ class PatchedStmtVisitor : public swift::StmtVisitor<ImplClass, StmtRetTy, Args.
 
 class StmtVisitor : public PatchedStmtVisitor<StmtVisitor> {
  public:
+  // SwiftDispatcher should outlive the StmtVisitor
   StmtVisitor(SwiftDispatcher& dispatcher) : dispatcher(dispatcher) {}
 
   template <typename E>

swift/extractor/visitors/TypeVisitor.h

@@ -7,6 +7,7 @@ namespace codeql {
 
 class TypeVisitor : public swift::TypeVisitor<TypeVisitor> {
  public:
+  // SwiftDispatcher should outlive the TypeVisitor
   TypeVisitor(SwiftDispatcher& dispatcher) : dispatcher(dispatcher) {}
 
   template <typename E>