Remove unnecessary thread suspension

Removed unnecessary thread suspension since it's already done by
ScopedGCCriticalSection. This also fixes the access of handles
without holding the mutator lock.

Added scoped traces to RegisterDexFile to help detect any delays
caused by blocking on GC from the ScopedGCCriticalSection.

Bug: 109720594
Test: test-art-host

Change-Id: I0bc7402eca7c8bff92d3522ccd30ca802bca2863