Minor EventTarget correctness issues

[domenic]

I just noticed some very minor things while idly browsing recent node commits. /cc @benjamingr.

• Version: 56e4460
• Subsystem: events

Per Web IDL, EventTarget.prototype[Symbol.toStringTag] should be a data property, not a getter. The commit above introduced it as a getter.

Note that url.js appears to do this correctly using the defineIDLClass function, which perhaps should be shared.

• Version: 2d071e7
• Subsystem: events

isTrusted should not have a setter. It should only have a getter, since it is declared as a readonly Web IDL attribute.

[benjamingr]

Thanks for noticing, I should have probably also used the primordial, I will make a PR to fix this.

[benjamingr]

This is probably also true for Event, I will fix it there too.