Move some fields in art::Thread to reduce maintenance burden.

Move fields `thread_local_start`, `thread_local_pos`,
`thread_local_end` and `thread_local_objects` before fields
`jni_entrypoints` and `quick_entrypoints` within
art::Thread, to avoid repetitive art::Thread field moves in
future CLs caused by the addition or deletion of entry
points.

Test: m test-art-host
test: m test-art-target (on ARM)
Change-Id: Ib67842e44a7f21a871ca4d1bb95dc6f7cfedc829