Revert to first-best-fit run/chunk allocation.

This effectively reverts 97c04a93838c4001688fe31bf018972b4696efe2 (Use
first-fit rather than first-best-fit run/chunk allocation.).  In some
pathological cases, first-fit search dominates allocation time, and it
also tends not to converge as readily on a steady state of memory
layout, since precise allocation order has a bigger effect than for
first-best-fit.

(cherry picked from upstream commit https://github.com/jemalloc/jemalloc/commit/aa2826621e1793db9faea31e803690ccbe36f14c)

Bug: 22172059
Change-Id: I3327939e1354c9a358dc54ce2b667feda890e42b