test: refactor test-fs-error-messages.js

• group tests by error type
• improve error validation for all messages
• use assert.throws instead of try and catch
• use arrow functions
• add missing test for readdir
• add missing test for readFileSync
• remove unnecessary variables

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)

test