Refactor map loading & saving (#34020)

diff --cc Content.IntegrationTests/Tests/SaveLoadMapTest.cs
index 1bfcd8ab608818ed5042cc93137a11fb991517e4,b96fbe5767351b737794340c0bb46831bed6fef9..eb3dc1472088d2187869fd1289d8ab8d1308a07f
--- 1/Content.IntegrationTests/Tests/SaveLoadMapTest.cs
--- 2/Content.IntegrationTests/Tests/SaveLoadMapTest.cs
+++ b/Content.IntegrationTests/Tests/SaveLoadMapTest.cs
@@@ -44,11 -45,11 +45,11 @@@ namespace Content.IntegrationTests.Test
                  {
                      var mapGrid = mapManager.CreateGridEntity(mapId);
                      xformSystem.SetWorldPosition(mapGrid, new Vector2(-8, -8));
 -                    mapSystem.SetTile(mapGrid, new Vector2i(0, 0), new Tile(2, (TileRenderFlag) 1, 254));
 +                    mapSystem.SetTile(mapGrid, new Vector2i(0, 0), new Tile(typeId: 2, flags: 1, variant: 254));
                  }
  
-                 Assert.Multiple(() => mapLoader.SaveMap(mapId, mapPath));
-                 Assert.Multiple(() => mapManager.DeleteMap(mapId));
+                 Assert.That(mapLoader.TrySaveMap(mapId, mapPath));
+                 mapSystem.DeleteMap(mapId);
              });
  
              await server.WaitIdleAsync();