pgsql: Move syncscan.c to src/backend/access/common.

Move syncscan.c to src/backend/access/common.

Since the tableam.c code needs to make use of the syncscan.c routines
itself, and since other block-oriented AMs might also want to use it one
day, it didn't make sense for it to live under src/backend/access/heap.

Reviewed-by: Andres Freund <andres(at)anarazel(dot)de>
Discussion: https://postgr.es/m/CA%2BhUKGLCnG%3DNEAByg6bk%2BCT9JZD97Y%3DAxKhh27Su9FeGWOKvDg%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/cb04ad498551dcdb91a834c2e8730cdf0b77e70a

Modified Files
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src/backend/access/common/Makefile | 1 +
src/backend/access/{heap => common}/syncscan.c | 6 +++---
src/backend/access/heap/Makefile | 1 -
src/backend/access/heap/heapam.c | 1 +
src/backend/access/heap/heapam_handler.c | 1 +
src/backend/access/table/tableam.c | 2 +-
src/backend/storage/ipc/ipci.c | 1 +
src/include/access/heapam.h | 6 ------
src/include/access/syncscan.h | 25 +++++++++++++++++++++++++
9 files changed, 33 insertions(+), 11 deletions(-)