pgsql: Stop including parsenodes.h in plannodes.h

Stop including parsenodes.h in plannodes.h

I added it by mistake in commit 7103ebb7aae8. To clean up, struct
MergeAction needs to be moved to primnodes.h from parsenodes.h. (This
forces us to also move OverridingKind to primnodes.h).

Having to add parsenodes.h to bootstrap.h as fallout is a bit
surprising, since nothing nominally needs it there. However, per
comments in bootscanner.l, it is needed so that YYSTYPE can be declared.
I think this only started with commit dac048f71ebb, but I didn't
actually verify that.

In passing, stop including parsenodes.h in tcopprot.h. Nothing needs it
there.

Per discussion on a patch by Ashutosh Bapat.

Reviewed-by: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Discussion: https://postgr.es/m/202311071106.6y7b2ascqjlz@alvherre.pgsql

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/615f5f6faa0fb659c4e20e1d2137a869cd33058b

Modified Files
--------------
src/backend/utils/adt/windowfuncs.c | 1 +
src/include/bootstrap/bootstrap.h | 1 +
src/include/nodes/parsenodes.h | 24 ------------------------
src/include/nodes/plannodes.h | 1 -
src/include/nodes/primnodes.h | 27 +++++++++++++++++++++++++++
src/include/tcop/tcopprot.h | 1 -
6 files changed, 29 insertions(+), 26 deletions(-)