Make transaction handling compatible with node-sqlite3-wasm

https://github.com/tndrle/node-sqlite3-wasm doesn't have transaction support so I've tried to implement it using SQL statements directly.

@hoelzro do you think this is right? Should we be rolling back the transaction in the finally clause? It would be nice to have tests in this area...

I looked at better-sqlite3's implementation - https://github.com/WiseLibs/better-sqlite3/blob/master/lib/methods/transaction.js

plugins/tiddlywiki/multiwikiserver/modules/sql-tiddler-database.js

@@ -500,16 +500,21 @@ Execute the given function in a transaction, committing if successful but rollin
 Calls to this function can be safely nested, but only the top-most call will actually take place in a transaction.
 */
 SqlTiddlerDatabase.prototype.transaction = function(fn) {
- try {
- const alreadyInTransaction = this.transactionDepth > 0;
- this.transactionDepth++;
- if(alreadyInTransaction) {
- return fn();
- } else {
- return this.db.transaction(fn)();
+ const alreadyInTransaction = this.transactionDepth > 0;
+ this.transactionDepth++;
+ if(alreadyInTransaction) {
+ return fn();
+ } else {
+ try {
+ this.runStatement(`BEGIN TRANSACTION`);
+ var result = fn();
+ this.runStatement(`COMMIT TRANSACTION`);
+ } catch(e) {
+ this.runStatement(`ROLLBACK TRANSACTION`);
+ } finally {
+ this.transactionDepth--;
  }
- } finally {
- this.transactionDepth--;
+ return result;
  }
 };