Refactor build utilities

Separated generic functions from build helpers.

Changed:
- Moved 'utils/*.js' to 'helpers/*.js'
- From 'utils/config.js':
  - Moved function `merge` to 'utils/index.js'.
  - Moved function `isObjectLike` to 'utils/index.js'.
- From 'utils/template.js':
  - Moved function `flatten` to 'utils/index.js'.
  - Moved function `escapeRegExp` to 'utils/index.js'.
- From 'tasks/styles.js':
  - Moved function `createPostCSSProcessor` to 'helpers/postcss.js' as `createProcessor`.
- Replaced function `Object.assign` with `merge` for task options parsing in all tasks.

build/helpers/config.js

@@ -0,0 +1,19 @@
+/**
+ * @file Provides simple user configuration options.
+ */
+
+import loconfig from '../../loconfig.json' assert { type: 'json' };
+import { merge } from '../utils/index.js';
+
+try {
+    const usrconfig = await import('../../loconfig.local.json', {
+        assert: { type: "json" },
+    });
+    usrconfig = usrconfig.default;
+
+    merge(loconfig, usrconfig);
+} catch (err) {
+    // do nothing
+}
+
+export default loconfig;