this change introduces enforcement of 'const-correctness' into implemented function graphs.
summary:
if you have a function declared in C++ like this:
UFUNCTION(BlueprintImplementableEvent)
int32 MyFunctionThatReturnsSomeValue() const;
if you implement that (BPIE) function in a Blueprint that's parented to that native class, it will now be flagged as 'const'. this makes any properties of 'self' read-only within the context of that graph, which means the compiler will emit an error if you try to set a property or otherwise call a non-const, non-static function with 'self' as the target.
if there happens to already be an implemented const function in a Blueprint that was in place prior to this change, the compiler will emit a warning instead of an error, in order to allow existing Blueprints that may currently be "violating" const within the context of a const BPIE function to still compile, while still alerting to issues that should probably be addressed.
notes:
1) this also applies to BlueprintNativeEvent (BPNE) implementations, and also when implementing BPIE/BPNE interface methods that are also declared as const
2) a const BPIE/BPNE function with no return value and no output parameters will be implemented as a "normal" impure function, and not as an event as in the non-const case
3) a const BPIE/BPNE function with a return value and/or output parameters will currently be implemented as a pure function, regardless of whether or not BlueprintCallable is specified
4) this CL also retains some consolidation of static function validation code that i had previously done, mostly to allow static functions to more easily be whitelisted for const function graphs
#codereview Nick.Whiting, Michael.Noland
[CL 2368059 by Phillip Kavan in Main branch]
