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

Revisa los ejemplos de /doc/api e inventaría los bloques de código mjs y cjs, señalando los casos que demuestren específicamente el comportamiento de CommonJS. Confirma con los maintainers el alcance y la convención de ESM como opción predeterminada antes de consolidar los ejemplos aptos en bloques js. Se considera terminado cuando se hayan eliminado los ejemplos duplicados y las demostraciones específicas de CJS sigan siendo precisas.