benchmark: add benchmark for object properties

Adds a benchmark to compare the speed of property setting/getting in
four cases:
- Dot notation: `obj.prop = value`
- Bracket notation with string: `obj['prop'] = value`
- Bracket notation with string variable: `obj[prop] = value`
- Bracket notation with Symbol variable: `obj[sym] = value`

PR-URL: https://github.com/nodejs/node/pull/10949


Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>