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

检查 /doc/api 下的示例，并盘点 mjs 和 cjs 代码块，记录明确展示 CommonJS 行为的情况。在将符合条件的示例整合到 js 代码块之前，与维护者确认范围以及默认使用 ESM 的约定。完成的标准是移除重复示例，同时确保 CJS 特有的演示仍然准确。