use Symbol.for instead of Symbol ctor

[devhawk]

I was debuging Transact using one of our demo apps. Because I was running Transact from the repo against a demo app w/ it's own version of Transact, it couldn't locate any of the handler endpoints. Because I was using two different copies of Transact, I ended up with two different sets of metadata key symbols:

dbos-transact/src/decorators.ts

Lines 78 to 80 in 6e97e1e

	const paramMetadataKey = Symbol("dbos:parameter");
	const methodMetadataKey = Symbol("dbos:method");
	const classMetadataKey = Symbol("dbos:class");

This PR switches these symbols from using Symbol's constructor to using Symbol.for.

Symbol('bar') !== Symbol('bar');
Symbol.for('bar') === Symbol.for('bar');

[maxdml]

For reference: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/for