Rename Memory::Lock() to Core_LockAgainstShutdown(), move it to Core

It stopped being about memory when CPU_Shutdown started holding it across the
whole teardown - it's what keeps kernel objects, the symbol map and the memory
map from being freed while another thread reads them. The old name invited the
reading that it locks memory *access*, which it has never done.

Memory::Reinit() now holds it across both halves rather than relying on
Memory::Shutdown()'s own acquire: between Shutdown() and Init() there is no
memory map at all, and a reader could slip into that gap.

Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01GZq8ZtJmFY7bkX5FVkr3P9

Core/MemMap.cpp

@@ -87,7 +87,6 @@ u32 g_PSPModel;
 
 static MemMapSetupFlags g_setupFlags;
 
-std::recursive_mutex g_shutdownLock;
 
 // We don't declare the IO region in here since its handled by other means.
 static MemoryView views[] = {
@@ -343,6 +342,9 @@ bool Init(MemMapSetupFlags flags) {
 void Reinit() {
 	_assert_msg_(PSP_GetBootState() == BootState::Complete, "Cannot reinit during startup/shutdown");
 	Core_NotifyLifecycle(CoreLifecycle::MEMORY_REINITING);
+	// Held across both halves: between Shutdown() and Init() there is no memory map at all, and a
+	// reader that only saw Shutdown()'s own acquire could slip into that gap.
+	CoreShutdownLock coreLock = Core_LockAgainstShutdown();
 	MemMapSetupFlags flags = g_setupFlags;
 	Shutdown();
 	Init(flags);
@@ -421,7 +423,7 @@ void DoState(PointerWrap &p) {
 }
 
 void Shutdown() {
-	std::lock_guard<std::recursive_mutex> guard(g_shutdownLock);
+	CoreShutdownLock coreLock = Core_LockAgainstShutdown();
 	u32 flags = 0;
 	MemoryMap_Shutdown();
 	base = nullptr;
@@ -432,21 +434,6 @@ bool IsActive() {
 	return base != nullptr;
 }
 
-// Wanting to avoid include pollution, MemMap.h is included a lot.
-MemoryInitedLock::MemoryInitedLock()
-{
-	g_shutdownLock.lock();
-}
-MemoryInitedLock::~MemoryInitedLock()
-{
-	g_shutdownLock.unlock();
-}
-
-MemoryInitedLock Lock()
-{
-	return MemoryInitedLock();
-}
-
 static Opcode Read_Instruction(u32 address, bool resolveReplacements, Opcode inst) {
 	if (!MIPS_IS_EMUHACK(inst.encoding)) {
 		return inst;