Use boot image extension for framework libraries.

This patch splits the system boot image in two parts:

  - The ART boot image. This is the primary boot image that is
    included in the ART apex and contains dexpreopted Core Libraries.

  - The framweork boot image extension. It depends on the ART boot
    image and contains framework libraries.

The third "apex" boot image (used in the JIT-zygote experiment)
remains unchanged; it is a monolithic primary boot image that
contains both libcore and framework libraries.

Dexpreopting of APKs now uses the framework boot image extension
(which in turn pulls in the ART boot image as a dependency).

Test: m
Test: phone boots:
    lunch aosp_walleye-userdebug && m \
        && adb reboot bootloader && fastboot flashall -w

Bug: b/119800099

Exempt-From-Owner-Approval: rebased after getting approval.

Change-Id: Ida40dfae8c83bf7c2e737d5c7ea418e1197ad826