Simplify WebView RELRO creation and handle more cases.

Instead of having the system server search for the absolute path to the
WebView's native .so file, simply pass the package name and library
filename to the RELRO creation process. The RELRO creation process can
then request a classloader that corresponds to that package, and use
that classloader to let the system search for the library itself using
the standard platform library search path logic.

This significantly simplifies the WebView code, but more importantly
enables the library to be found even if it's not actually present in the
main WebView APK and is instead stored in a shared library APK: our
previous code was never updated to handle this new case when the
platform introduced it.

As a side effect of no longer searching for the library, we also no
longer discover the size of the library, and thus cannot use the size to
calculate the amount of address space to reserve. This has been replaced
with a fixed size: 100MB for 32-bit processes (the previous default size
for when the size had not yet been calculated), and 1GB for 64-bit
processes. We do not anticipate WebView ever needing more than 100MB of
virtual address space for its native library on 32-bit platforms; it
currently uses about 44MB.

The unit tests covering the complex library searching logic have been
removed, as the functionality they are testing no longer exists.

Bug: 110790153
Test: WebView-related CTS and GTS tests
Change-Id: Icc7bcd0a2b33f4dbf26d0d663e098c9e207281a5