Modifications to the UI can only be made from the main thread.
Since {N} 5.3.0 all debugger protocol messages are processed
by the worker thread that receives them in iOS.
refs #7219, https://github.com/NativeScript/ios-runtime/pull/1101
* add initial implementation of the dom agent for ios
* add implementation of the css agent for ios
* refactor devtools inspector methods to somewhat accomodate ios and android
patch elements dom-node tests to test for ios too
* fix android dom-node test
* fix ios dom-node-tests to mock the ios devtools inspector properly
* fix: minor changes
