Use minifyJS options hash

[rmharrison]

Do you want a PR to use the minifyJS options hash?

I think it will cause confusion if options have to be moved from the minifyJS hash to the ember-cli-uglify hash. I'd just allow the enable, exclude and uglify options to be set in either minifyJS or ember-cli-uglify (precedence), as I'm unaware of other minifyJS options that would need to be passed.

For on-boarding, documentation 1 would also need to be updated if minifyJS hash is dropped.

[rwjblue]

I think supporting enabled in minifyJS and warning if we detect any other options would be fine.

[rwjblue]

In retrospect (3 years later 😞), we should have done this when you opened this issue @rmharrison. I'm sorry about that.

At this point, most folks are passing options in ember-cli-uglify now, so adding support for minifyJS would actually not be great (due to the amount of time that has elapsed).

I tried to ensure we didn't make the same mistake during the rename to ember-cli-terser (over in #230).