Remove overlay logic from package manager and parser

Remove overlay logic from package manager and parser

Consolidate all knowledge about overlays to the overlay manager (except
static RROs that target "android": these are handled from native code in
order to be loaded as part of Zygote boot).

This removes the ability to overlay AndroidManifest.xml. There are some
use-cases where overlaying a manifest makes sense [e.g. changing an
app's label or icon or what components should be enabled by default] but
the opposite is also true [e.g. permissions]. Support for manifests can
be introduced again gradually with these goals in mind:

  - should not happen during parsing [which represents the immutable
    truth as read from disk]

  - should happen during scanning [which applies mutable settings to a
    parsed package]

  - be limited in what can be modified

Bug: 78808368
Test: builds, boots
Change-Id: I12c16fce65b1e68876f0c9acd7e2a61405e64435