pgsql: Revert "Refactor CopyAttributeOut{CSV,Text}() to use a callback

Revert "Refactor CopyAttributeOut{CSV,Text}() to use a callback in COPY TO"

This reverts commit 2889fd23be56, following a discussion with Andres
Freund as this callback, being called once per attribute when sending a
relation's row, can involve a lot of indirect function calls (more
attributes to deal with means more impact). The effects of a dispatch
at this level would become more visible when improving the per-row code
execution of COPY TO, impacting future potential performance
improvements.

Discussion: https://postgr.es/m/20240206014125.qofww7ew3dx3v3uk@awork3.anarazel.de

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/1aa8324b81fa4979ffdc6ccf81d560eac9446948

Modified Files
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src/backend/commands/copyto.c | 47 ++++++++++++++-----------------------------
1 file changed, 15 insertions(+), 32 deletions(-)