Microsoft.Data.Sqlite: Use multi-thread mode

Previously, the default mode (usually Serialized) was used. Since ADO.NET connections are generally not thread safe, this caused unnecessary lock checking in SQLite.

Note, this will break compatibility with versions compiled with SQLITE_THREADSAFE=0. However, we plan to add a connection pool in this release which, I suspect, will also break compatibility with those versions anyway.

Resolves #22330

src/Microsoft.Data.Sqlite.Core/SqliteConnection.cs

@@ -174,7 +174,7 @@ public override void Open()
             }
 
             var filename = ConnectionOptions.DataSource;
-            var flags = 0;
+            var flags = SQLITE_OPEN_NOMUTEX;
 
             if (filename.StartsWith("file:", StringComparison.OrdinalIgnoreCase))
             {