#jira UE-6304 - Source Control: Add the ability to commit file deletions from the editor
#reviewedby Thomas.Sarkanen
[CL 2446774 by Richard TalbotWatkin in Main branch]
API break: added new pure virtual ISourceControlProvider::UsesChangelists()
API break: added new pure virtual ISourceControlState::FindHistoryRevision(const FString&)
API break: added new pure virtual ISourceControlRevision::GetRevision()
Implementing a Git provider requires us to be able to display revisions that are not indices as Git revisions are hashes. This updates the relvant code to allow us to display these revisions correctly.
[CL 2411986 by Thomas Sarkanen in Main branch]
* Multicast delegate Add* calls now return FDelegateHandles, and Remove* calls are now all deprecated, except for a new Remove function which takes a FDelegateHandle.
* New FConsoleManager::RegisterConsoleVariableSink_Handle and UnregisterConsoleVariableSink_Handle functions which work in terms of FConsoleVariableSinkHandle.
* Timer calls which don't take FTimerHandles are deprecated.
* FTicker::AddTicker now returns an FDelegateHandle and is removed by an overloaded Remove function.
* DEFINE_ONLINE_DELEGATE* macros now define _Handle variants of the Add/Remove functions which return/take handles.
* Various other handle-based registration changes.
* Some unity build fixes.
* Some simplification of delegate code.
* Fixes for lots of existing code to use handle-based registration and unregistration.
#codereview robert.manuszewski
[CL 2400883 by Steve Robb in Main branch]
