Time out and dump stacks from R8 processes after 30 minutes

R8 processes are sometimes hanging on the build servers.  Wrap R8 with
run_with_timeout to dump the stacks with jstack and kill the process
after 30 minutes.  Switch from running with the r8-compat-proguard
shell script to running the jar directly so that jstack gets the pid
of the java process.

Bug: 181095653
Test: m checkbuild
Test: m NetworkStackNextIntegrationTests
Test: m USE_RBE=true RBE_R8=true RBE_R8_EXEC_STRATEGY=remote NetworkStackNextIntegrationTests
Change-Id: If6996bd8eb39c7a8453d79e825004339c009ade2