core: Initial pass on synchronous pragma

This adds support for "OFF" and "FULL" (default) synchronous modes. As
future work, we need to add NORMAL and EXTRA as well because
applications expect them.

parser/src/ast.rs

@@ -1360,6 +1360,8 @@ pub enum PragmaName {
     QueryOnly,
     /// Returns schema version of the database file.
     SchemaVersion,
+    /// Control database synchronization mode (OFF | FULL | NORMAL | EXTRA)
+    Synchronous,
     /// returns information about the columns of a table
     TableInfo,
     /// enable capture-changes logic for the connection