Add functional shim for Zotero.Promise.method()

For translation.

chrome/content/zotero/xpcom/bluebirdShim.mjs

@@ -13,10 +13,29 @@ export class BluebirdShimPromise extends Promise {
 	}
 	
 	static method(fn) {
-		// TEMP: "Implement" this with a stub until we update zotero/translate
-		// Don't bother with synchronous resolution - this is just enough to get the client to load
+		// ONLY exists for translator code that needs synchronous resolution.
+		// Please don't use this anywhere else. It's a bad idea!
 		return function (...args) {
-			return Promise.resolve(fn.apply(this, args));
+			try {
+				let returnValue = fn.apply(this, args);
+				let promise;
+				let isResolved = false;
+				if (returnValue && returnValue.then) {
+					promise = returnValue;
+				}
+				else {
+					promise = Promise.resolve(returnValue);
+					isResolved = true;
+				}
+				if (typeof promise.isResolved === 'undefined') {
+					promise.then(() => isResolved = true, () => {});
+					promise.isResolved = () => isResolved;
+				}
+				return promise;
+			}
+			catch (e) {
+				return Promise.reject(e);
+			}
 		};
 	}
 }