Added IsValid to check wether the object is valid and bound to a scripting runtime.
Merging CL#2645093 using UE4-To-UE4-LauncherDev
[CL 2645229 by Keli Hlodversson in Main branch]
* Untangle mutual dependencies between objects and constructor order (OPP-3858):
* FWebBrowserWindow no longer keeps a reference to FWebBrowserHandler.
* CefBrowserWindow is created before creating FWebBrowserWindow and passed to its constructor.
* FWebBrowserViewport no longer has a reference back to the viewport widget.
* Cleaned how some platform specific paths were defined during module initialization.
* Sets current thread name (back) to GameThread after initializing CEF (UE-5165)
* Adopted changes from UT (with some modifications):
* Enable on-disk caching and persisting cookies when requested by server.
* Added product name and engine version to user agent request header.
* Ensure UStruct parameters passed by value to FWebJSFunctions are copied when constructing the argument list and not just their address.
*SWebBrowser scripting: Add support for passing TMap<FString, T> to FWebJSFunction objects.
Note: since the struct serializer does not yet support maps, this only works for arguments passed directly to the function object and not UStruct members nor function return values. OPP-3861
* Add support for passing a reference to the JS promise object implicitly created when calling UFunctions to provide for a way to report runtime errors back to it instead of just passing the return value.
* This also allows for implementing async functionality as the promise object can be saved and used after the UFunction has returned.
Merging CL#2633955, CL#2634077, CL#2634226, CL#2635540, CL#2636167, and CL#2636262 using UE4-To-UE4-LauncherDev
[CL 2636308 by Keli Hlodversson in Main branch]
Add support for passing TArray<T> as an argument to a FWebJSFunction.
rb: Justin.Sargent
Merging CL#2627633 using UE4-To-UE4-LauncherDev
[CL 2633907 by Keli Hlodversson in Main branch]
Implement JS integration via a subset of UObject scripting functionality and custom CEF Messages
JIRA: OPP-3240
rb: Justin.Sargent
[CL 2601283 by Keli Hlodversson in Main branch]
