Dex compiler: re-enable method pattern matching

The dex compiler's mechanism to detect simple methods and emit
streamlined code was disabled during the last big restructuring
(there was a question of how to make it useful for Portable as
well as Quick).  This CL does not address the Portable question,
but turns the optimization back on for Quick.

See b/9428200

Change-Id: I9f25b41219d7a243ec64efb18278e5a874766f4d