Add a method to get the default webview provider

The method will be used by settings to get which package to keep enabled.
Also, this defines which package we will fallback to for the modified findPreferredWebViewPackage.

Test:  atest com.android.server.webkit.WebViewUpdateServiceTest

Bug: 308907090
Change-Id: Ib5efef1b04ba2fe098ef2695e56902818f0a20c9
6 files changed