Add XML documentation for Android.Service.QuickAccessWallet

The `Android.Service.QuickAccessWallet` namespace contains **249** `To be added` placeholders in source XML documentation (excluding `docs\xml\index.xml`).

Example command:

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

## Update log

- 2026-09-10: Refreshed the placeholder scan from **237** to **249** (increased by **12**). Related documentation PRs: [#644](https://github.com/dotnet/android-api-docs/pull/644).

Start by running the provided rg command against docs\xml to list the Android.Service.QuickAccessWallet XML documentation placeholders, then inspect the matching namespace and API entries. Done means replacing the 249 reported “To be added” placeholders with documentation and confirming the refreshed scan no longer reports them, while excluding docs\xml\index.xml.

Vom Indexierungsmodell aus dem Issue-Text verfasst.