Move public libraries list to a separate source file

Functions for reading the public libraries list are moved out of
library_namespace.cpp to public_libraries.cpp.

In addition, library-local symbols are moved from android namespace to
android::nativeloader namespace.

Bug: 130388701
Test: build & pass presubmit tests
Change-Id: If82419598304d56d29bfec4ef553443c788d0f53
diff --git a/libnativeloader/native_loader.cpp b/libnativeloader/native_loader.cpp
index ed98714..eeee077 100644
--- a/libnativeloader/native_loader.cpp
+++ b/libnativeloader/native_loader.cpp
@@ -40,6 +40,8 @@
 
 namespace {
 #if defined(__ANDROID__)
+using android::nativeloader::LibraryNamespaces;
+
 constexpr const char* kApexPath = "/apex/";
 
 std::mutex g_namespaces_mutex;