Allow the WebView native library to have dependencies.

The WebView native library has so far only depended on native libraries
that were already loaded by the zygote, and has only shipped a single
.so file in its APK. Splitting the code into multiple libraries worked,
but only the top-level library would have its RELRO section shared,
causing a memory regression.

To avoid this regression if we do decide to split up the native code in
future, load the native library using the new RESERVED_ADDRESS_RECURSIVE
flag in the linker, which means that any depended-upon libraries will
also be loaded into the reserved address region and will have their
RELRO sections saved and reused.

Fixes: 128623590
Test: tested manually with modified WebView
Change-Id: I19ee3ff971e8dcd1c683f94af304abf918860a10