Fix jl_gc_wb_genericmemory_copy_boxed not advancing src/dest ptr (#61852)
Claude Opus 4.7 xhigh spotted this one when I was making some unrelated
changes (I'm impressed!). #57252/378a42508d4 introduced this bug when
extracting the code for `jl_gc_wb_genericmemory_copy_boxed` from
`jl_genericmemory_copyto`: the caller assumes `src_p` and `dest_p` will
be updated to point to the remaining elements `memmove_refs` must copy,
but we no longer mutate them. I had Claude turn them into pointers, so
they are updated like before.
Nifty PoC:
```julia
dest = Any[nothing for i=1:16]
for i in 1:2
GC.gc(true)
GC.gc(false)
end
src = vcat(Any[nothing], Any[Ref(100 * i) for i=1:15])
copyto!(dest, src)
for (i, (x, y)) in enumerate(zip(dest, src))
if x !== y
println("dest[$i] = $x, expected src[$i] = $y")
end
end
```
julia
e0923156 - Fix jl_gc_wb_genericmemory_copy_boxed not advancing src/dest ptr (#61852)
