The delegate SKActionTimingFunction has the wrong return type

[logbase2]

Steps to Reproduce

1. Look at the documentation: https://developer.xamarin.com/api/type/SpriteKit.SKActionTimingFunction/
2. Notice the remarks say "Application developers should assign this delegate to a method that returns 0 for a time value of 0, and 1 for a time value of 1."
3. Notice that the return type of the delegate is Void.

Expected Behavior

The delegate should have a float return type, to match the iOS behavior and the Xamarin documentation.

Actual Behavior

SKActionTimingFunction is currently not useable. If you create a function/lambda expression with the return type required by the delegate (Void), then the delegate compiles but the function is useless. The whole purpose of the function is to return a float value from 0 to 1, which is impossible with a Void function.

Environment

Visual Studio for Mac

=== Visual Studio Community 2017 for Mac ===

Version 7.4.2 (build 12)
Installation UUID: 7ec21259-98d2-4bc8-9b0c-658488837fc9
Runtime:
	Mono 5.8.1.0 (2017-10/6bf3922f3fd) (64-bit)
	GTK+ 2.24.23 (Raleigh theme)

	Package version: 508010000

=== NuGet ===

Version: 4.3.1.4445

=== .NET Core ===

Runtime: /usr/local/share/dotnet/dotnet
Runtime Versions:
	2.0.5
	2.0.0
SDK: /usr/local/share/dotnet/sdk/2.1.4/Sdks
SDK Versions:
	2.1.4
	2.0.0
MSBuild SDKs: /Library/Frameworks/Mono.framework/Versions/5.8.1/lib/mono/msbuild/15.0/bin/Sdks

=== Xamarin.Profiler ===

Version: 1.6.1
Location: /Applications/Xamarin Profiler.app/Contents/MacOS/Xamarin Profiler

=== Apple Developer Tools ===

Xcode 9.3 (14154)
Build 9E145

=== Xamarin.Mac ===

Version: 4.2.1.28 (Visual Studio Community)

=== Xamarin.iOS ===

Version: 11.9.1.24 (Visual Studio Community)
Hash: f62de472
Branch: xcode9.3
Build date: 2018-03-29 19:30:53-0400

=== Xamarin.Android ===

Version: 8.2.0.16 (Visual Studio Community)
Android SDK: /Users/joshua/Library/Android/sdk
	Supported Android versions:
		4.4    (API level 19)
		4.4.87 (API level 20)
		6.0    (API level 23)
		7.1    (API level 25)

SDK Tools Version: 26.1.1
SDK Platform Tools Version: 27.0.1
SDK Build Tools Version: 27.0.3

Java SDK: /usr
java version "1.8.0_40"
Java(TM) SE Runtime Environment (build 1.8.0_40-b25)
Java HotSpot(TM) 64-Bit Server VM (build 25.40-b25, mixed mode)

Android Designer EPL code available here:
https://github.com/xamarin/AndroidDesigner.EPL

=== Xamarin Inspector ===

Version: 1.4.0
Hash: b3f92f9
Branch: master
Build date: Fri, 19 Jan 2018 22:00:34 GMT
Client compatibility: 1

=== Build Information ===

Release ID: 704020012
Git revision: 0d8e3f0a4d683771f17959739956fa09c7ba21e3
Build date: 2018-03-30 10:45:17-04
Xamarin addins: 958839ea56ab1e331caf7c92b6ad50fb9e6ee9d2
Build lane: monodevelop-lion-d15-6

=== Operating System ===

Mac OS X 10.13.4
Darwin 17.5.0 Darwin Kernel Version 17.5.0
    Mon Mar  5 22:24:32 PST 2018
    root:xnu-4570.51.1~1/RELEASE_X86_64 x86_64

=== Enabled user installed addins ===

Internet of Things (IoT) development (Preview) 7.1

Build Logs

Example Project (If Possible)

VS bug #610350, VS bug #610351

[mandel-macaque]

Confirming the issue, as per Apple docs we have:

float (^SKActionTimingFunction)(float time);

https://developer.apple.com/documentation/spritekit/skactiontimingfunction?language=objc