Allow the shared_relro creation process to make calls to PackageManager,
so that it can create a classloader corresponding to the current WebView
implementation. This avoids needing to pass an absolute path to the
native library to the process, which required that the calling code
duplicate existing logic in the framework to find the library and
resulted in bugs and inconsistencies.

Bug: 110790153
Test: WebView-related CTS and GTS tests
Change-Id: I9902bb0400e2a800021dac06278151c8541d458f