Core: Fix trim in Android<4.1
Css: Don't check fill-opacity in Android 2.3, it's not supported
Event: Blacklist the onbeforeunload test in Android 2.3

Similarly to iOS, Android 2.3 has the onbeforeunload property on window
but doesn't support the event. This commit blacklists the test there as well.
Effects: Don't check fill-opacity in Android 2.3, it's not supported
Support: Skip style-based tests when element.style is undefined

Fixes #14785
Ref #13754
Ref badcd1b6f301e6253405f17759c1270549a34e12
Support: Reduce size

Ref a7ea12a9a7c696a14455bfe4bfebf984dd329832
Data: move element cache to element[expando]

- avoid explicit data.discard() cleanup calls
- explicitly remove the data.events property
- reduces code footprint

Fixes #11570