Update LoadedFragmentMetadata::create to return a shared pointer. (#5214)

[SC-51612](https://app.shortcut.com/tiledb-inc/story/51612/use-make-shared-to-create-loadedfragmentmetadata)

Using `make_shared` to create the shared pointer is more efficient
because the control plane is located next to the object.

---
TYPE: NO_HISTORY

Author: teo-tsirpanis

tiledb/sm/fragment/loaded_fragment_metadata.cc

@@ -75,15 +75,16 @@ LoadedFragmentMetadata::LoadedFragmentMetadata(
 /*                API                */
 /* ********************************* */
 
-LoadedFragmentMetadata* LoadedFragmentMetadata::create(
+shared_ptr<LoadedFragmentMetadata> LoadedFragmentMetadata::create(
     FragmentMetadata& parent,
     shared_ptr<MemoryTracker> memory_tracker,
     format_version_t version) {
   if (version <= 2) {
-    return tdb_new(V1V2PreloadedFragmentMetadata, parent, memory_tracker);
+    return make_shared<V1V2PreloadedFragmentMetadata>(
+        HERE(), parent, memory_tracker);
   }
 
-  return tdb_new(OndemandFragmentMetadata, parent, memory_tracker);
+  return make_shared<OndemandFragmentMetadata>(HERE(), parent, memory_tracker);
 }
 
 uint64_t LoadedFragmentMetadata::persisted_tile_size(

tiledb/sm/fragment/loaded_fragment_metadata.h

@@ -95,7 +95,7 @@ class LoadedFragmentMetadata {
    *     metadata corresponds to.
    * @param version The format version of the fragment
    */
-  static LoadedFragmentMetadata* create(
+  static shared_ptr<LoadedFragmentMetadata> create(
       FragmentMetadata& parent,
       shared_ptr<MemoryTracker> memory_tracker,
       format_version_t version);