buffer: refactor buffer exports

• Refactor buffer exports to use module.exports = {} pattern
• Migrate most errors to use internal/errors _{refack: crossed off, as this was done in #13976}

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• commit message follows commit guidelines

Affected core subsystem(s)

buffer