Dump the entire state of WebViewUpdateService on demand.

It is especially useful to know which is the current WebView package but
we also add some other state to be able to debug WebViewUpdateService.

Bug: 32307028
Test: Run 'adb shell dumpsys webviewupdate' and inspect printed
contents.
Test: Take bug report and inspect the 'webviewupdate' dump section.
Change-Id: I79c2cda87ea7633a915eae5de3c3015b18ed6d7c