Increase the interval used by grunt watch to reduce CPU usage

[jeremyfelt]

grunt watch appears to use around 40% of my CPU when sitting idle. By default, ​grunt-contrib-watch uses a 100ms interval. Several of the groups in our _watch config specify an interval of 2 seconds, but others defer to the default.

In my local environment (non-VM), if I add options: { interval: 2000 } to the config, colors, test, and phpunit groups, grunt watch CPU usage stays consistently within 2 to 5% at idle.

See ​this related discussion on the grunt-contrib-watch project

If I change all configurations to 1 second, grunt watch CPU usage stays at around 9%.

I'm attaching a patch that applies only the interval addition to each of the other groups.

[netweb]

In 44241.2.diff​ I've moved options: { interval: 2000 } to the top-level option that applies to all the _watch sub-tasks rather than adding it to each sub-task, all watch tasks will default to this 2s value.

Locally my mid-2014 MacBook Pro sees CPU usage from grunt watch sit at ~4%

[jeremyfelt]

In 43324:

Built/Test Tools: Increase grunt watch interval on all files.

Significantly reduces Grunt's CPU usage when grunt watch is in an idle/watching state.

Props netweb.
Fixes #44241.