tools: modernize and optimize doc/addon-verify.js

Checklist

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

Modernize:

• Replace var with const / let.
• Replace common functions with arrow functions.
• Use destructuring.
• Use String.prototype.padStart(), String.prototype.endsWith().

Optimize:

• Reduce function calls.
• Reduce intermediate variables.
• Cache retrieved object properties.
• Move RegExp declaration out of a cycle.
• Simplify RegExps.
• Replace RegExp with string when string suffices.
• Remove conditions that cannot be false.
• Replace for..in with Object.keys().forEach().

Also, eliminate needlessly complicated function chains:

• ondone callback only checks errors;
• if there is an error, it is called once and throws, then script exits;
• if there are no errors, it is noop;
• so there is no need to wrap it into once() function;
• and there is no need to call it without errors;
• we can eliminate it and replace with throw where an error occurs;
• we can also replace onprogress callback with console.log in place;
• at last, we can eliminate waiting counter and once() utility.

The new script produces results identical to the old ones.