pgsql: Move logic related to WAL replay of Heap/Heap2 into its own file

Move logic related to WAL replay of Heap/Heap2 into its own file

This brings more clarity to heapam.c, by cleanly separating all the
logic related to WAL replay and the rest of Heap and Heap2, similarly
to other RMGRs like hash, btree, etc.

The header reorganization is also nice in heapam.c, cutting half of the
headers required.

Author: Li Yong
Reviewed-by: Sutou Kouhei, Michael Paquier
Discussion: https://postgr.es/m/EFE55E65-D7BD-4C6A-B630-91F43FD0771B@ebay.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/00c76cf21c42c17e60e73a87dea0d1b4e234d9da

Modified Files
--------------
src/backend/access/heap/Makefile | 1 +
src/backend/access/heap/heapam.c | 1339 ---------------------------------
src/backend/access/heap/heapam_xlog.c | 1339 +++++++++++++++++++++++++++++++++
src/backend/access/heap/meson.build | 1 +
src/include/access/heapam.h | 25 +
5 files changed, 1366 insertions(+), 1339 deletions(-)