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/Android.bp b/libnativeloader/Android.bp
index 4d65b50..3b77a9e 100644
--- a/libnativeloader/Android.bp
+++ b/libnativeloader/Android.bp
@@ -30,6 +30,7 @@
         android: {
             srcs: [
                 "library_namespaces.cpp",
+                "public_libraries.cpp",
             ],
             shared_libs: [
                 "libdl_android",