Add comments to describe some builtins

Bug: v8:11879
Change-Id: Ia0047b701e77b6e766984de527e817874d95f38e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2989102Reviewed-by: Santiago Aboy Solanes <solanes@chromium.org>
Reviewed-by: Shu-yu Guo <syg@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75488}

src/builtins/builtins-definitions.h

@@ -131,7 +131,9 @@ namespace internal {
   ASM(JSEntry, Dummy)                                                          \
   ASM(JSConstructEntry, Dummy)                                                 \
   ASM(JSRunMicrotasksEntry, RunMicrotasksEntry)                                \
+  /* Call a JSValue. */                                                        \
   ASM(JSEntryTrampoline, JSTrampoline)                                         \
+  /* Construct a JSValue. */                                                   \
   ASM(JSConstructEntryTrampoline, JSTrampoline)                                \
   ASM(ResumeGeneratorTrampoline, ResumeGenerator)                              \
                                                                                \
@@ -149,6 +151,8 @@ namespace internal {
   TFS(OrderedHashTableHealIndex, kTable, kIndex)                               \
                                                                                \
   /* Interpreter */                                                            \
+  /* InterpreterEntryTrampoline dispatches to the interpreter to run a */      \
+  /* JSFunction in the form of bytecodes */                                    \
   ASM(InterpreterEntryTrampoline, JSTrampoline)                                \
   ASM(InterpreterPushArgsThenCall, InterpreterPushArgsThenCall)                \
   ASM(InterpreterPushUndefinedAndArgsThenCall, InterpreterPushArgsThenCall)    \