move classes out of native_loader.cpp

native_loader.cpp is too crowded. Move the classes
NativeLoaderNamespaces and LibraryNamespaces out of native_loader.cpp to
their own source files.

This change does not alter any functionality.

Bug: 130388701
Test: m, presubmit tests
Change-Id: Ibc61ec0dc6727af7cac865b1971ebf1befac6855
5 files changed