When building from source, require nodeJS >= 14.15.0

The longterm support of node@12 will run out next month. Over a year ago we started recommending node@14, as of recent we started using node@16 on our development machines and CI.

For a future eslint upgrade we need to drop support for node@12. Updates to our minimum required node version can happen outside of the normal breaking release cycle, as it is just needed for building from source and is no runtime requirement.

• node@12 -> node@14 !52099 (merged)
• node@14 -> node@16 !81372 (merged)

Changelog: other