pgsql: Use NameData datatype for slotname in stats.

Use NameData datatype for slotname in stats.

This will make it consistent with the other usage of slotname in the code.
In the passing, change pgstat_report_replslot signature to use a structure
rather than multiple parameters.

Reported-by: Andres Freund
Author: Vignesh C
Reviewed-by: Sawada Masahiko, Amit Kapila
Discussion: https://postgr.es/m/20210319185247.ldebgpdaxsowiflw@alap3.anarazel.de

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/cca57c1d9bf7eeba5b81115e0b82651cf3d8e4ea

Modified Files
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src/backend/postmaster/pgstat.c           | 32 +++++++++++++++----------------
src/backend/replication/logical/logical.c | 13 ++++++++++---
src/backend/replication/slot.c            |  7 ++++++-
src/backend/utils/adt/pgstatfuncs.c       |  2 +-
src/include/pgstat.h                      | 11 ++++-------
5 files changed, 36 insertions(+), 29 deletions(-)