Add XML documentation for Android.Media.Browse

The `Android.Media.Browse` namespace contains **68** `To be added` placeholders in source XML documentation (excluding `docs\xml\index.xml`).

Example command:

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

## Update log

- 2026-09-10: Refreshed the placeholder scan from **66** to **68** (increased by **2**). Related documentation PRs: [#644](https://github.com/dotnet/android-api-docs/pull/644).

Start with the documented files under docs\xml\Android.Media.Browse\ and the ns-Android.Media.Browse.xml file. Run the issue's rg scan to inspect all 68 "To be added" placeholders, then replace them with accurate XML documentation. Done means the namespace's placeholders are documented and the scan finds none, excluding docs\xml\index.xml.

Written by the indexing model from the issue text.