Add XML documentation for Android.OS.Strictmode

The `Android.OS.Strictmode` namespace contains **258** `To be added` placeholders in source XML documentation (excluding `docs\xml\index.xml`).

Example command:

```powershell
rg -n -i --glob 'Android.OS.Strictmode/**' --glob 'ns-Android.OS.Strictmode.xml' 'to be added' docs\xml
```

Use the provided rg command under docs\xml to locate the 258 `To be added` placeholders in Android.OS.Strictmode source XML documentation, excluding docs\xml\index.xml. Read the surrounding entries to determine the needed API descriptions, then verify that no matching placeholders remain in the namespace files.

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