Split dex_file_loader_test

Into DexFileLoader and ArtDexFileLoader portions.  This is the last test
refactoring before moving libdexfile out of the runtime directory.

Bug: 22322814
Test: make -j 50 test-art-host
Change-Id: I7568a7b444fb110f64614f2066df6eb5ab3a5c69
6 files changed