[vm] Skip caching of function entry points in Thread in JIT mode

Cached entry points of core library functions are only used
in AOT mode (JIT mode uses Function/Code objects instead of entry
points in order to call those functions).

This change removes storing entry points into the Thread.
It fixes TSAN error which reports a data race between JIT compilation
which installs Code and caching of entry points when scheduling
a thread.

TEST=ci
Fixes #49194
Issue: #48378

Change-Id: Ib109118df414cd722001dad363e9e05a94ab0556
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/247501
Commit-Queue: Alexander Markov <[email protected]>
Reviewed-by: Slava Egorov <[email protected]>
Reviewed-by: Daco Harkes <[email protected]>

Author: alexmarkov

runtime/vm/isolate.cc

@@ -614,12 +614,14 @@ Thread* IsolateGroup::ScheduleThreadLocked(MonitorLocker* ml,
     thread->isolate_ = nullptr;
     thread->isolate_group_ = this;
     thread->field_table_values_ = nullptr;
+#if defined(DART_PRECOMPILED_RUNTIME)
     if (object_store() != nullptr) {
 #define INIT_ENTRY_POINT(name)                                                 \
   thread->name##_entry_point_ = Function::EntryPointOf(object_store()->name());
       CACHED_FUNCTION_ENTRY_POINTS_LIST(INIT_ENTRY_POINT)
 #undef INIT_ENTRY_POINT
     }
+#endif  // defined(DART_PRECOMPILED_RUNTIME)
     ASSERT(heap() != nullptr);
     thread->heap_ = heap();
     thread->set_os_thread(os_thread);