Give full access to system libs from other system libs.

In particular this addresses the case when an app without a shared
namespace loads a shared system library that in turn loads a system JNI
library.

Give full access both ways between /system and /system_ext libraries,
and add a shared system_ext library and loading from system_ext to test
that.

Test: atest libnativeloader_e2e_tests
Bug: 237577392
Change-Id: Ief4e24dadbadd26c5602c9e593276fae01bd7038
14 files changed