Revise ext/standard/tests/file test suite

Description

Occasionally, there are still test conflicts, and a couple of tests are marked as obscure_filename conflicting. Furthermore, some of the tests do not necessarily clean up properly after execution (they unlink some created files during test execution only). Also, some tests appear to have POSIX and Windows variants, although that doesn't seem to be necessary. See e.g. #16722 and #16854.

Ideally, all tests should only create and delete files which either have the same base name as the test case, or are placed in a directory with the base name of the test case. Since this may lead to overlong paths, we may need to take some shortcuts there (possibly using shorter test case names).

In any way, this test suite should be cleaned up/improved.

まず ext/standard/tests/file と #16722 および #16854 の関連する例を確認してください。競合、obscure_filename のマーキング、クリーンアップの動作、POSIX/Windows のバリアントを洗い出してください。完了の条件は、テストスイートがそのファイルまたはディレクトリを一貫して分離し、不要なバリアントを使わずに作成したファイルを削除することです。