CoreBluetooth.AdvertismentData.ServiceData always returns null

### Steps to Reproduce

1. Create a program that uses CoreBluetooth to scan advertising data.
2. Scan a device that includes service data in the advertising data.
3. Try to use [CoreBluetooth.AdvertismentData.ServiceData](https://docs.microsoft.com/en-us/dotnet/api/corebluetooth.advertisementdata.servicedata?view=xamarin-ios-sdk-12#CoreBluetooth_AdvertisementData_ServiceData) to access the service data.

### Expected Behavior

It should return a dictionary containing the service data.

### Actual Behavior

It returns `null`.

### Environment

```
=== Visual Studio Professional 2019 for Mac ===

Version 8.10.1 (build 71)
Installation UUID: 8707ccd4-8a47-4c78-a9b7-855f9311eab2
GTK+ 2.24.23 (Raleigh theme)
Xamarin.Mac 6.18.0.23 (d16-6 / 088c73638)

Package version: 612000140

=== Mono Framework MDK ===

Runtime:
Mono 6.12.0.140 (2020-02/51d876a041e) (64-bit)
Package version: 612000140

=== Roslyn (Language Service) ===

3.10.0-4.21269.26+029847714208ebe49668667c60ea5b0a294e0fcb

=== NuGet ===

Version: 5.9.0.7134

=== .NET Core SDK ===

SDK: /usr/local/share/dotnet/sdk/6.0.100-preview.4.21255.9/Sdks
SDK Versions:
6.0.100-preview.4.21255.9
5.0.301
5.0.203
5.0.201
5.0.103
5.0.101
3.1.410
3.1.409
MSBuild SDKs: /Applications/Visual Studio.app/Contents/Resources/lib/monodevelop/bin/MSBuild/Current/bin/Sdks

=== .NET Core Runtime ===

Runtime: /usr/local/share/dotnet/dotnet
Runtime Versions:
6.0.0-preview.4.21253.7
5.0.7
5.0.6
5.0.4
5.0.3
5.0.1
3.1.16
3.1.15

=== .NET Core 3.1 SDK ===

SDK: 3.1.410

=== Xamarin.Profiler ===

Version: 1.6.12.26
Location: /Applications/Xamarin Profiler.app/Contents/MacOS/Xamarin Profiler

=== Updater ===

Version: 11

=== Xamarin.Android ===

Version: 11.3.0.1 (Visual Studio Professional)
Commit: xamarin-android/d16-10/22fc2b3
Android SDK: Not found

=== Microsoft OpenJDK for Mobile ===

Java SDK: Not Found

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

=== Android SDK Manager ===

Version: 16.10.0.12
Hash: e240b8c
Branch: remotes/origin/d16-10
Build date: 2021-06-01 18:26:34 UTC

=== Android Device Manager ===

Version: 16.10.0.14
Hash: e340248
Branch: remotes/origin/d16-10
Build date: 2021-06-01 18:26:52 UTC

=== Apple Developer Tools ===

Xcode 12.5 (18205)
Build 12E262

=== Xamarin.Mac ===

Version: 7.14.0.3 (Visual Studio Professional)
Hash: 17fdcf569
Branch: d16-10
Build date: 2021-05-20 15:46:14-0400

=== Xamarin.iOS ===

Version: 14.20.0.3 (Visual Studio Professional)
Hash: 17fdcf569
Branch: d16-10
Build date: 2021-05-20 15:46:15-0400

=== Xamarin Designer ===

Version: 16.10.0.119
Hash: 36a2d986f
Branch: remotes/origin/d16-10
Build date: 2021-06-02 19:41:34 UTC

=== Build Information ===

Release ID: 810010071
Git revision: 3664adb3ec17b7a29476110bb1c6f7083d43b1ab
Build date: 2021-06-08 13:22:15-04
Build branch: release-8.10

=== Operating System ===

Mac OS X 10.16.0
Darwin 20.5.0 Darwin Kernel Version 20.5.0
Tue May 4 22:32:58 PDT 2021
root:xnu-7195.121.3~4/RELEASE_X86_64 x86_64
```

### Build Logs

### Example Project (If Possible)