[disassembler] Better support for roots

In particular, output root name instead of root value when detecting accesses
to roots table. For example:

  REX.W cmpq [r13+0x80] (root (0x391473a00569 <Map[16]>)),rbx
  REX.W movq rdi,[r13+0x18] (root (0x391473a007b9 <Map>))
  REX.W movq rdi,[r13-0x20] (root (0x391473a005b9 <the_hole>))

turns into

  REX.W cmpq [r13+0x80] (root (heap_number_map)),rbx
  REX.W movq rdi,[r13+0x18] (root (fixed_array_map))
  REX.W movq rdi,[r13-0x20] (root (the_hole_value))

Bug: v8:8238
Change-Id: I0f7bdcb7774a2fe450f930c1bc2f3ccd03064201
Reviewed-on: https://chromium-review.googlesource.com/c/1317823Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57262}

src/disassembler.cc

@@ -132,12 +132,7 @@ const char* V8NameConverter::RootRelativeName(int offset) const {
     RootIndex root_index =
         static_cast<RootIndex>(offset_in_roots_table / kPointerSize);
 
-    HeapStringAllocator allocator;
-    StringStream accumulator(&allocator);
-    isolate_->root(root_index)->ShortPrint(&accumulator);
-    std::unique_ptr<char[]> obj_name = accumulator.ToCString();
-
-    SNPrintF(v8_buffer_, "root (%s)", obj_name.get());
+    SNPrintF(v8_buffer_, "root (%s)", RootsTable::name(root_index));
     return v8_buffer_.start();
 
   } else if (static_cast<unsigned>(offset - kExtRefsTableStart) <