[MERGE #5374 @kfarnung] Copy FunctionBody display names if necessary

Merge pull request #5374 from kfarnung:user/kfarnung/literalstring

In cached bytecode scenarios the display name can come directly from
the bytecode buffer. Since it's not owned by the engine that data needs
to be copied to ensure that the buffer remains valid.

OS#17525348

Author: kfarnung

lib/Runtime/Base/FunctionBody.cpp

@@ -1033,11 +1033,32 @@ namespace Js
         }
     }
 
+    // Returns a raw pointer to the display name which may not have a well-known lifetime. It's safer to use
+    // GetExternalDisplayNameObject if the end goal is to create an object anyway.
     const char16* ParseableFunctionInfo::GetExternalDisplayName() const
     {
         return GetExternalDisplayName(this);
     }
 
+    // Allocates a new JavascriptString object containing the display name associated with the FunctionBody.
+    JavascriptString* ParseableFunctionInfo::GetExternalDisplayNameObject(ScriptContext* scriptContext) const
+    {
+        const char16* name = GetExternalDisplayName();
+
+        if (!GetDisplayNameIsRecyclerAllocated() && !IsConstantFunctionName(name))
+        {
+            // The string is allocated in memory that we don't directly control the lifetime of. Copy the string to
+            // ensure that the buffer remains valid for the lifetime of the object.
+            return Js::JavascriptString::NewCopySz(name, scriptContext);
+        }
+        else
+        {
+            // Use the incoming buffer directly to create the object. This only works when the lifetime of the data is
+            // static or GC allocated.
+            return Js::JavascriptString::NewWithSz(name, scriptContext);
+        }
+    }
+
     RegSlot
     FunctionBody::GetLocalsCount()
     {

lib/Runtime/Base/FunctionBody.h

@@ -1096,7 +1096,7 @@ namespace Js
         // this is also now being used for function.name.
         const char16* GetShortDisplayName(charcount_t * shortNameLength);
 
-        bool GetDisplayNameIsRecyclerAllocated() { return m_displayNameIsRecyclerAllocated; }
+        bool GetDisplayNameIsRecyclerAllocated() const { return m_displayNameIsRecyclerAllocated; }
 
         bool IsJitLoopBodyPhaseEnabled() const
         {
@@ -1678,6 +1678,7 @@ namespace Js
         void CopyNestedArray(ParseableFunctionInfo * other);
 
         const char16* GetExternalDisplayName() const;
+        JavascriptString* GetExternalDisplayNameObject(ScriptContext* scriptContext) const;
 
         //
         // Algorithm to retrieve a function body's external display name. Template supports both