[heap] Refactor methods and nested class of ConcurrentMarkingVisitor

This CL moves a few methods and nested class SlotSnapshottingVisitor
from ConcurrentMarkingVisitor to ConcurrentMarkingVisitorUtility.

Methods in ConcurrentMarkingVisitorUtility are now static and instead have a Visitor parameter.

This is preparatory work for adding a
YoungGenerationConcurrentMarkingVisitor class, which will be able to
reuse members of ConcurrentMarkingVisitorUtility.

Bug: v8:13012
Change-Id: I503c20e655578031018a2e37dd92c1d61bbe1686
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3779677
Commit-Queue: Leon Bettscheider <bettscheider@google.com>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81931}

src/heap/marking-visitor.h

@@ -220,6 +220,11 @@ class MarkingVisitorBase : public HeapVisitor<int, ConcreteVisitor> {
 #endif
   }
 
+  bool is_shared_heap() { return is_shared_heap_; }
+
+  // Marks the object grey and pushes it on the marking work list.
+  V8_INLINE void MarkObject(HeapObject host, HeapObject obj);
+
  protected:
   ConcreteVisitor* concrete_visitor() {
     return static_cast<ConcreteVisitor*>(this);
@@ -259,8 +264,6 @@ class MarkingVisitorBase : public HeapVisitor<int, ConcreteVisitor> {
   // list and visits its header. Returns the size of the descriptor array
   // if it was successully marked as black.
   V8_INLINE int MarkDescriptorArrayBlack(DescriptorArray descriptors);
-  // Marks the object grey and pushes it on the marking work list.
-  V8_INLINE void MarkObject(HeapObject host, HeapObject obj);
 
   V8_INLINE void AddStrongReferenceForReferenceSummarizer(HeapObject host,
                                                           HeapObject obj) {