pgsql: Move instrumentation-related structs to instrument_node.h

Move instrumentation-related structs to instrument_node.h

Some structs and enums related to parallel query instrumentation had
organically grown scattered across various files, and were causing
header pollution especially through execnodes.h. Create a single file
where they can live together.

This only moves the structs to the new file; cleaning up the pollution
by removing no-longer-necessary cross-header inclusion will be done in
future commits.

Co-authored-by: Álvaro Herrera <alvherre(at)kurilemu(dot)de>
Co-authored-by: Mario González <gonzalemario(at)gmail(dot)com>
Reviewed-by: Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>
Discussion: https://postgr.es/m/202510051642.wwmn4mj77wch@alvherre.pgsql
Discussion: https://postgr.es/m/CAFsReFUr4KrQ60z+ck9cRM4WuUw1TCghN7EFwvV0KvuncTRc2w@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/2defd00062555c03f7ac4d8f004b98b36b876c5d

Modified Files
--------------
contrib/bloom/blscan.c | 1 +
src/backend/access/gin/ginscan.c | 1 +
src/backend/access/gist/gistget.c | 1 +
src/backend/access/hash/hashsearch.c | 1 +
src/backend/access/nbtree/nbtsearch.c | 1 +
src/backend/access/spgist/spgscan.c | 1 +
src/backend/utils/sort/tuplesort.c | 2 +-
src/include/access/genam.h | 23 +---
src/include/executor/instrument_node.h | 211 +++++++++++++++++++++++++++++++++
src/include/nodes/execnodes.h | 140 ----------------------
src/include/utils/tuplesort.h | 37 +-----
11 files changed, 220 insertions(+), 199 deletions(-)