SF: Do not duplicate fences per layer per frame

Convert the unique_fd of RenderEngineResult (and futures thereof) into
sp<Fence> such that postFramebuffer does not duplicate release/present
fences.

Remove a few copies of shared futures/pointers with std::move.

Bug: 232436803
Test: simpleperf (-33% cycles in sys_dup)
Change-Id: Ia7c6c8333a712441f3612fb5c720ea2932799636