refactor: convert to ECMAScript where necessary

Also drop @league-of-foundry-developers/foundry-vtt-types.

src/handlebars/handlebars-partials.js

@@ -4,7 +4,11 @@
 //
 // SPDX-License-Identifier: MIT
 
-export async function registerHandlebarsPartials(): Promise<void> {
+/**
+ * Register the Handlebars partials for DS4.
+ * @returns {Promise<void>} A promise that resolves once all partials have been registered
+ */
+export async function registerHandlebarsPartials() {
     const templatePaths = [
         "systems/ds4/templates/sheets/actor/components/actor-header.hbs",
         "systems/ds4/templates/sheets/actor/components/actor-progression.hbs",