`Android.Telecom.RemoteConference` has wrong type

[jonpryor]

Context: #1078 (comment)

API-24 introduced android.telecom.RemoteConference.getConnectionProperties().

In $(TargetFrameworkVersion) v7.0 (API-24), we bound this as as type CallProperty:

https://github.com/xamarin/xamarin-android/blob/2c2d47c4a28eeb398500a8c0a9a0a803324de014/src/Mono.Android/methodmap.csv#L2100

24, android.telecom, RemoteConference, getConnectionProperties, return, Android.Telecom.CallProperty

In $(TargetFrameworkVersion) v7.1 (API-25), we bound this as ConnectionProperties:

https://github.com/xamarin/xamarin-android/blob/2c2d47c4a28eeb398500a8c0a9a0a803324de014/src/Mono.Android/methodmap.csv#L2144

25, android.telecom, RemoteConnection, getConnectionProperties, return, Android.Telecom.ConnectionProperties

Question: Why do we have three separate enumifications for this method? (There's a 2nd API-25 one two lines below the link above.)

Regardless, this mismatch introduces an inter-api-level inconsistency around the type of RemoteConference.ConnectionProperties. The result is that any assemblies which build against v7.0 and run in v7.1+ will throw a MissingMethodException.

We should fix things so that all API levels -- API-24+ -- bind RemoteConference.ConnectionProperties as ConnectionProperties

[atsushieno]

As I commented at #1078 (comment) those constants didn't exist in API Level 24 (see the comment for more details).

[jonpryor]

@atsushieno suggested:

(2) mark those constants as if they existed since API Level 24.

I think we should go for (2a): Introduce an empty enum in API-24:

#if ANDROID_24 && !ANDROID_25
namespace Android.Telecom {
    public enum ConnectionProperties {
    }
}
#endif

We do similar things elsewhere:

• https://github.com/xamarin/xamarin-android/blob/2c2d47c4a28eeb398500a8c0a9a0a803324de014/src/Mono.Android/Android.Views/View.cs

[atsushieno]

Not quite like an additional code, but more like metadata fixup trick.