add nopreload option in public.libraries.txt

A lib with 'nopreload' option in public.libraries.txt is not preloaded
during zygote. This is useful for seldom used public libraries; they
don't contribute to the zygote startup time and only affect the apps
that they are used.

Bug: 132911956
Test: libnativeloader_test
Change-Id: I6f97c90e6721aec7f2f96c8fc7b963b34f8edd3e