Support LOCAL_JACK_ENABLED := javac_frontend

Allow working around Jack bugs by using javac to compile *.java
to class files, and then pass through Jack for desugaring,
proguarding, and dexing.

Also make ANDROID_COMPILE_WITH_JACK=false override LOCAL_JACK_ENABLED.

Bug: 37483961
Test: m -j checkbuild
Test: Add LOCAL_JACK_ENABLED := javac_frontend to a target
Change-Id: I2189055aac9deccc36b8eab8e949796dddadf7a1