Use native implementations of Object.keys and Array.isArray

[legobeat]

json-stable-stringify is already failing CI tests on Node.js version <=0.6 (https://github.com/ljharb/json-stable-stringify/actions/runs/7545755257/job/20542261535).

Node.js 0.10 went EOL in 2016.

The shims contain code permuting globals, which causes noise in static analysis and may be an cause issues if inadvertently triggered.

• BREAKING: Increase minimum Node.js version from 0.4 to 0.10
  • Remove Node.js v0.6 and v0.8 from test matrix (v0.4 was already not tested despite support being indicated)
• Replace isarray with native Array.isArray
• Replace object-keys with native Object.keys

[ljharb]

The 0.6 failure is because node itself can't compile, not because the project doesn't pass on it.

EOL status is irrelevant.

The code paths we use here don't mutate globals, so it shouldn't break any static analysis worth relying on.

Additionally, Object.keys has a ton of bugs in a ton of engines, including browsers, so using the package is the safest approach by a long shot.