Previously, `electronSwitches` only accepted strings. This PR adds
support for object entries, allowing switches with values:
```js
electronSwitches: [
"no-sandbox",
{ "js-flags": "--max-old-space-size=8192" }
]
```
I decided to put the logic into a helper file so it can be unit-tested
independently, since electron.js itself requires a live Electron
environment and cannot be tested in isolation.
Fixes#4159
e55b11be5d