Don't pass static libs to r8

r8 gets the static libs in the program jar, it shouldn't also get
them as library jars.  Keep a separate classpath for dexing that
includes libs but not static_libs.

Bug: 222468116
Test: m checkbuild
Test: TestD8
Test: TestR8
Change-Id: Icca3393f496cbcadcc633f3b156761e6c145f975