This change adds support for dexpreopting standalone system server
jars from prebuilts.
Bug: 203198541
Test: -
1. Add a standalone system server jar (e.g., by patching
aosp/1906158)
2. Build and drop a module SDK and an APEX.
3. Build a system image from prebuilts.
4. See the odex and vdex files generated in
$ANDROID_PRODUCT_OUT/system/framework/oat/
Change-Id: I8f4eaed10a1053cd560b8583efa12dc495f58db1