BufferQueues: clean up BufferItemConsumer constructors

These currently use flags that muddy up client code. We've added nice
new BufferItemConsumer::create methods, so lets use those and clean
things up.

BYPASS_IGBP_IGBC_API_REASON=warren buffers

Bug: 398822412
Flag: EXEMPT refactor
Test: builds, presubmit
Change-Id: Idbc9047638239ae4971e3fb142d70000b2911a9c