Fix preopting Soong apps

dex_preopt_odex_install.mk should always be included, it handles
setting a default value for LOCAL_DEX_PREOPT.
Use dexpreopt-copy-jar when preopting to strip the dex file if
necessary.

Bug: 115967961
Test: m SystemUI
Change-Id: I74f77ed0e88a67043836407261f3845a16cbaf37