Make --debuggable rely on JIT code.

Removes -Xfully-deoptable in the process, which was added as a
temporary workaround until this CL.
Partial revert of https://android-review.googlesource.com/#/c/302232/

Makes things consistent with existing infrastructure:

- Parse the --debuggable from the compiler options, just like
  --compiler-filter.

- Add DEBUG_JAVA_DEBUGGABLE, passed by the zygote, for debuggable apps.

- Java debuggable now solely relies on JIT for simplicity.

- Debugging under userdebug for non-java-debuggable apps is still
  best effort.

Test: test-art-host, jdwp

bug: 28769520
Change-Id: Id0593aacd85b9780da97f20914a50943957c858f