Add XML documentation for Android.Net.IpSec.Ike.Exceptions

The `Android.Net.IpSec.Ike.Exceptions` namespace contains **126** `To be added` placeholders in source XML documentation (excluding `docs\xml\index.xml`).

Example command:

```powershell
rg -n -i --glob 'Android.Net.IpSec.Ike.Exceptions/**' --glob 'ns-Android.Net.IpSec.Ike.Exceptions.xml' 'to be added' docs\xml
```

Run the provided rg command from the repository root to enumerate the 126 placeholders under docs\xml for Android.Net.IpSec.Ike.Exceptions. Review the matching namespace XML files and replace each “To be added” entry with appropriate documentation, excluding docs\xml\index.xml. Done means no matching placeholders remain in the targeted namespace files.

索引モデルが issue の本文から書いたものです。