Move jacocoagent into the bootclasspath

Move jacocoagent out of core-libart and into its own jar on the
bootclasspath.

Test: m -j EMMA_INSTRUMENT=true
Test: https://android-build.googleplex.com/builds/view-workplan?viewType=Table&workplanId=L19400000103297394&nodeType=Trybot
Change-Id: I9e6e3dc59dba8b93685d59b258d4ebc7835eab8b