[K/N][New MM] Move RunInNewThread to the main ThreadSupport.hpp

Some of unit-tests for the C++ part of the stdlib will require
thread state switching. In the new MM, we already have a helper
function that allows us to scopely initialize the memory subsystem
for a separate thread. This patch makes this helper available
for tests in the main runtime module by moving it to the main
ThreadSupport.hpp.

kotlin-native/runtime/src/mm/cpp/Memory.cpp

@@ -99,8 +99,7 @@ extern "C" void RestoreMemory(MemoryState*) {
 }
 
 extern "C" void ClearMemoryForTests(MemoryState* state) {
-    auto* threadData = FromMemoryState(state)->Get();
-    threadData->ClearForTests();
+    state->GetThreadData()->ClearForTests();
 }
 
 extern "C" RUNTIME_NOTHROW OBJ_GETTER(AllocInstance, const TypeInfo* typeInfo) {