`.env` file support issue tracker

This is a follow-up of dotenv support pr to track the development process, and answer some questions that require a general discussion for making the decision to implement them.

Todos:

• Precisely define the syntax of .env files, and consider a better format not based on ini
• Supporting absolute paths for .env file https://github.com/nodejs/node/pull/51425
• Should we support multiple --env-file through the CLI? (cc @GeoffreyBooth) https://github.com/nodejs/node/pull/49542
• Support multi-line values https://github.com/nodejs/node/pull/51289
• Follow up after @tniessen's PR has landed to main https://github.com/nodejs/node/pull/49213
• Should we add a programmatic API? If yes, what would be the use-case? (cc @cjihrig) https://github.com/nodejs/node/pull/51476

Questions:

• Should we merge NODE_OPTIONS if both environment variable and .env version exist? Currently, we prefer environment variable over .env configuration. (cc @ljharb) https://github.com/nodejs/node/pull/49217
• Should we throw if .env file does not exist? We currently follow the default behavior of dotenv package and do not throw. (cc @MoLow)

Please feel free to edit this issue in case there are more questions that needs to be answered.

cc @nodejs/tsc

This issue is a discussion tracker for Node.js .env support, with completed items linked to pull requests rather than a named file or test. Review the linked dotenv-related pull requests and remaining issue history first; the listed questions are marked resolved, so there is no clearly defined remaining change or completion test here.