Proper IPC wrapper for WebViewUpdateService.

Introduce a proper IPC client wrapper class for WebViewUpdateService
that can be used instead of directly consuming the AIDL interface.

The existing android.webkit.WebViewUpdateService wrapper has a bad API
and will be deprecated in future; in the meantime it will forward calls
to the new wrapper.

Bug: 319292658
Test: with flag enabled, atest CtsWebkitTestCases
Change-Id: I682a75a43eeebec26aa2d08b620b2f69bcfe0667