Restore legacy permalink behavior using :filepath pattern - #5661

How to test

git clone -b filepath-permalink https://github.com/dimaslanjaka/hexo.git
cd hexo
npm install
npm test

Thanks for working on a backward-compatible permalink option. I agree that a dedicated :filepath pattern is a reasonable approach, but I found a few issues that should be addressed before merging:

1. The new test imports Hexo from 'hexo'. The repository cannot resolve itself by package name in this context, so the test fails with TS2307: Cannot find module 'hexo'. Please use:

   import Hexo from '../../../lib/hexo';

2. The implementation hard-codes the default source/ directory. With a custom configuration such as source_dir: content, _posts/nested/foo.md produces:

   content/_posts/nested/foo.html
   

   instead of:

   nested/foo.html
   

3. Draft sources are not handled. _drafts/nested/foo.md currently produces _drafts/nested/foo.html, so the URL changes after the post is published.

Since Post.source already contains the path relative to source_dir, the implementation could be simplified to:

const relativeSourcePath = data.source
  .replace(/\\/g, '/')
  .replace(/^_(?:posts|drafts)\//, '')
  .replace(/\.[^/.]+$/, '');

Please also add regression tests for a custom source_dir and an _drafts/ source. I tested this approach against the existing permalink tests plus those two cases, and all 22 related tests passed.

One more note: no GitHub Actions checks are currently reported for this PR, despite the CI checkbox being marked as completed. Rebasing onto the latest master should allow the current checks to run.