[Patch] Build the heap more efficient in tuplesort.c

Hi hackers,

Now we build the heap by using tuplesort_heap_insert(), which has a sift-up every call.

To make it more efficient, I want to add tuplesort_heap_insert_unordered() and tuplesort_heap_build()
just like binaryheap_add_unordered() and binaryheap_build().

Thoughts?

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Regards,
ChangAo Chen