Sqlite: Add variadic bind and write functions

You can now write

SqliteWriteStatement statement("UPDATE test SET name=?, number=?
                                WHERE rowid=?", database);

statement.write("see", 7.23, 1);

and

SqliteWriteStatement statement("UPDATE test SET name=@name, number=@number
                                WHERE rowid=@id", database);

statement.writeNamed("@name", "see", "@number", 7.23, "@id", 1);

This is more type safe than using variants and performant too.

Change-Id: Ie1ed2a6d326b956be5c4ec056214f3f5b1531f45
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/libs/sqlite/sqlitedatabase.h

@@ -41,6 +41,7 @@ class SQLITE_EXPORT SqliteDatabase
 {
     friend class SqliteAbstractTransaction;
     friend class SqliteStatement;
+    friend class SqliteBackend;
 
 public:
     SqliteDatabase();
@@ -66,9 +67,10 @@ public:
 
     void execute(Utils::SmallStringView sqlStatement);
 
+    SqliteDatabaseBackend &backend();
+
 private:
     void initializeTables();
-    SqliteDatabaseBackend &backend();
 
 
 private: