Switch boot jars package check to using dex jars

The switch to use dex jars instead of class jars means that a boot jar
that is defined by a dex_import module will now be checked against the
package_allowed_list.txt so it is possible that it will detect
previously unreported problems.

Test: m check-boot-jars - for failing and passing cases
Bug: 171479578
Bug: 125517186
Change-Id: Ie614898dade0fb43c9418d7afb9138169db6f097