[memory] Move "Local\\" prefix to win impl

CreateFileMappingHandle now takes shared memory name without a prefix.
The doc of shm_open recommends not using slashes and prefixing with "/".
The prefixing has been moved to the os implementation layer.
Invocations of CreateFileMappingHandle were all using "Local\\" so these
prefixes were removed.

src/xenia/cpu/backend/x64/x64_code_cache.cc

@@ -63,8 +63,7 @@ bool X64CodeCache::Initialize() {
   }
 
   // Create mmap file. This allows us to share the code cache with the debugger.
-  file_name_ =
-      fmt::format("Local\\xenia_code_cache_{}", Clock::QueryHostTickCount());
+  file_name_ = fmt::format("xenia_code_cache_{}", Clock::QueryHostTickCount());
   mapping_ = xe::memory::CreateFileMappingHandle(
       file_name_, kGeneratedCodeSize, xe::memory::PageAccess::kExecuteReadWrite,
       false);