esm: revert format name to "cjs" over "commonjs"

This reverts the change originally made in https://github.com/nodejs/node/pull/16874, returning the "format" name to "cjs" instead of "commonjs".

There was some complaint over consistency of the new name form, so if we do want to change this should aim to get it in before that gets released.

Note the documentation change has already been released here, while the code change hasn't yet.

//cc @devsnek @MylesBorins @targos @jdalton

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

esm