ART: Native support for multidex

Native support for zip files with multiple classesX.dex.

Works by explicitly looking for those files in ascending order. As
these files have no file system representation for themselves,
introduce synthetic dex locations: the name of the originating file
plus a colon plus the name of the dex file, e.g., test.jar:classes2.dex.

Opening a zip dex file will return all dex files in this way. This
keeps the changes to dex2oat minimal.

To hide multidex/synthetic names from the Java layer, let the handle
of dalvik.system.DexFile refer to a vector of DexFile objects. When
opening a location, test possible synthetic names and add them to the
vector. Thus, the original multidex jar in the classpath will be
associated with all embedded dex files.

Change-Id: I0de107e1369cbc94416c544aca3b17525c9eac8b