Migrate to ECMAScript Modules

Migrate the usage of CommonJS specific code and imports to ESM.  Roughly
summarised this:
- Changes all require() calls to import statement or expressions.
- Changes usage of module.exports to export statements.
- Replaces require.resolve with import.meta.resolve.
- Replaces conditional imports with conditional subpath imports.
- Replaces module === require.main with import.meta.main.
- Adds the full filename with extention to all relative imports.
- Changes all usage of __dirname and __filename to their import.meta
  equivalents.
- Sets "type": "module" in package.json files.
- Removes usage of "use strict".
- Adds .ts an an alias of .js for the webpack build.

Due to differences in how require and import resolves files the plugin
entrypoints will have to include the filename and extension after this
migration in order to work.

test/lib/ModStore.test.js

@@ -1,15 +1,14 @@
-"use strict";
-const assert = require("assert").strict;
-const path = require("path");
-const fs = require("node:fs/promises");
-const stream = require("node:stream");
-const JSZip = require("jszip"); // Added for creating mock zips
+import assert from "node:assert/strict";
+import path from "node:path";
+import fs from "node:fs/promises";
+import stream from "node:stream";
+import JSZip from "jszip"; // Added for creating mock zips
 
 // Capture native fetch before any potential mocks are applied
 const nativeFetch = global.fetch;
 
-const { ModStore, ModInfo, ModVersionEquality } = require("@clusterio/lib"); // Adjust path based on compiled output
-const { externalTest } = require("../integration");
+import { ModStore, ModInfo, ModVersionEquality } from "@clusterio/lib"; // Adjust path based on compiled output
+import { externalTest } from "../integration/index.js";
 
 const MODS_DIR = path.join("temp", "test", "mod_store", "mods");
 const CACHE_FILE = path.join(MODS_DIR, "mod-info-cache.json");