Proposal: Remove ESM/CJS duality from code samples in API docs

Since the introduction of ESM to Node.js core, we have been providing togglable ESM/CJS code examples in the API docs.

These examples differ only in the lines of code containing core imports, but the entire codeblocks need duplicating due to the limitations of the web renderer, leading to whole reams of duplicated cruft across /doc/api. The documentation space is extremely patchy as to which examples are just ESM, just CJS, or both. We occasionally get very kind contributors submitting PRs to double-up existing CJS-only code examples, but these are not good uses of reviewer time.

Almost invariably, it is incredibly obvious as to how to convert an ESM import from a builtin module into a CJS import, or vice versa.

I suggest that we:

• get rid of ```mjs and ```cjs blocks in favour of a single ```js block
• canonicalise ESM imports as the example paradigm of choice, unless a example is specifically demonstrating something CJS-specific

/doc/api 配下の例を確認し、mjs と cjs のコードブロックを一覧化して、CommonJS の動作を特に示しているケースを記録します。対象範囲と ESM をデフォルトとする規約を maintainer に確認してから、対象となる例を js ブロックに統合します。重複した例が削除され、CJS 固有のデモンストレーションが正確なまま維持されていれば完了です。