fix(utils): Fix false-positive circular references when normalizing Event objects

[lobsterkatie]

When captureException is passed a non-Error object, we do our best to extract as much data as we can from that object. (That's what leads to the much-maligned "Non-Error exception [or promise rejection] captured with keys x, y, and z" error message.)

A common case in which this occurs is when code of the form Promise.reject(someEvent) runs - common enough, in fact, that we handle Event objects separately. Specifically, we capture the event's type, target (the element which caused the event), and currentTarget (the element with the event listener on it) properties (none of which are enumerable), along with anything else on the event which is enumerable. For most events, that "anything else" includes only one property: isTrusted, a boolean indicating whether or not the event is the result of a user action.

For a long time, though, isTrusted has been showing up not as a boolean but as [Circular ~]. It turns out that's because when we try to grab the enumerable property values, we end up grabbing the entire event instead. (It's only shown up in the isTrusted value, but only because that's the only enumerable property on most Events.) This fixes that, and adds a test for pulling data out of Event objects.

[github-actions]

size-limit report

Path	Size
@sentry/browser - CDN Bundle (gzipped)	21.57 KB (+0.03% 🔺)
@sentry/browser - Webpack	22.57 KB (+0.04% 🔺)
@sentry/react - Webpack	22.6 KB (+0.03% 🔺)
@sentry/browser + @sentry/tracing - CDN Bundle (gzipped)	28.99 KB (+0.02% 🔺)