Cache all platform aconfig packages in PlatformAconfigPackage

This change utilizes zygote caching all platform aconfig package in
PlatformAconfigPackage. Zygote will load all platform aconfig packages
and stores them in PlatformAconfigPackage.

The benefits of this change are

1. PlatformAconfigPackageInteral has faster package loading, since it
   can directly get the flag package from PlatformAconfigPackage,
   instead of reading from the mapped file.
2. Flag read won't cause disk restrict mode failure

Test: atest aconfig.test aconfig_storage_read_functional
aconfig_storage_file.test.java
Bug: 386382756
Flag: EXEMPT refactor

Change-Id: I0f42b72073e5a410619f5dc17ffb2890e670a5ff