ART: Add thread dump to dex2oat watchdog

To improve timeout investigations, add thread dumping to the dex2oat
watchdog.

This is a double-edged sword. To be really robust, we probably need
a second watchdog to kill the the first if it gets stuck dumping. So
consider this CL temporary.

Bug: 62337922
Test: m test-art-host-gtest_dex2oat_test
Test: m test-art-host
Change-Id: I2cef6c5978c7d8e487168ce8c0c5380e667c3fbc