pgsql: Refactor to make common functions in proto.c and worker.c.

Refactor to make common functions in proto.c and worker.c.

This is a non-functional change only to refactor code to extract some
replication logic into static functions.

This is done as preparation for the 2PC streaming patch which also shares
this common logic.

Author: Peter Smith
Reviewed-By: Amit Kapila
Discussion: https://postgr.es/m/CAHut+PuiSA8AiLcE2N5StzSKs46SQEP_vDOUD5fX2XCVtfZ7mQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/91f9861242cd7dcf28fae216b1d8b47551c9159d

Modified Files
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src/backend/replication/logical/proto.c  |  42 ++++++++++---
src/backend/replication/logical/worker.c | 101 +++++++++++++++++++------------
2 files changed, 95 insertions(+), 48 deletions(-)