feat: external config loading

+refactor many pieces

packages/webpack5/src/helpers/externalConfigs.ts

@@ -0,0 +1,36 @@
+import path from 'path';
+import fs from 'fs';
+import dedent from 'ts-dedent';
+import * as lib from '../index';
+import { error, info } from './log';
+import { getAllDependencies, getDependencyPath } from './dependencies';
+
+export function applyExternalConfigs() {
+	getAllDependencies().forEach((dependency) => {
+		const packagePath = getDependencyPath(dependency);
+		const configPath = path.join(packagePath, 'nativescript.webpack.js');
+
+		if (fs.existsSync(configPath)) {
+			info(`Discovered config: ${configPath}`);
+
+			try {
+				const externalConfig = require(configPath);
+
+				if (typeof externalConfig === 'function') {
+					externalConfig(lib);
+				} else {
+					// todo: warn user
+					// todo: perhaps support exported objects to merge into config?
+				}
+			} catch (err) {
+				error(
+					dedent`
+					Unable to apply config: ${configPath}.
+					Error is:
+				`,
+					err
+				);
+			}
+		}
+	});
+}