pgsql: Refactor heapam.c adding heapgettup_initial_block function

Refactor heapam.c adding heapgettup_initial_block function

Here we adjust heapgettup() and heapgettup_pagemode() to move the code
that fetches the first block number to scan out into a helper function.
This removes some code duplication.

Author: Melanie Plageman
Reviewed-by: David Rowley
Discussion: https://postgr.es/m/CAAKRu_bvkhka0CZQun28KTqhuUh5ZqY=_T8QEqZqOL02rpi2bw@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/fb1a59de0c52609653166aafc6ce8679a9cfe54b

Modified Files
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src/backend/access/heap/heapam.c | 223 ++++++++++++++++++---------------------
1 file changed, 102 insertions(+), 121 deletions(-)