WIP Fix MediaContent-related API not being generated

[marius-bughiu]

WIP (do not merge)
This is mostly generated with Claude and I need to test it first.
Fixes: #973
Needed for: marius-bughiu/Plugin.AdMob#78

Problem

The IMediaContent interface was not being generated because it contained obfuscated methods (zza(), zzb()) that referenced internal types (com.google.android.gms.internal.ads.zzbfs). This caused the binding generator to skip the entire interface.

As a result, the MediaContent property on NativeAd, MediaView, and related classes was unavailable to .NET developers.

Solution

Added <remove-node> rules to the Metadata.xml transform files to exclude the problematic obfuscated methods from the MediaContent interface:

<remove-node path="/api/package[@name='com.google.android.gms.ads']/interface[@name='MediaContent']/method[@name='zza']" />
<remove-node path="/api/package[@name='com.google.android.gms.ads']/interface[@name='MediaContent']/method[@name='zzb']" />

New API Surface

Android.Gms.Ads.IMediaContent interface with:

• AspectRatio
• CurrentTime
• Duration
• HasVideoContent
• MainImage
• VideoController

MediaContent property now available on:

• NativeAd
• MediaView
• INativeCustomFormatAd