Put genbki.pl output into src/include/catalog/ directly

With the makefile rules, the output of genbki.pl was written to
src/backend/catalog/, and then the header files were linked to
src/include/catalog/.

This patch changes it so that the output files are written directly to
src/include/catalog/.  This makes the logic simpler, and it also makes
the behavior consistent with the meson build system.  For example, a 
file like schemapg.h is now mentioned only in

src/include/catalog/{meson.build,Makefile,.gitignore}

where before it was mentioned in (checks ...)

src/backend/catalog/.gitignore
src/backend/catalog/Makefile
src/include/Makefile
src/include/catalog/.gitignore
src/include/catalog/meson.build

Also, the list of catalog files is now kept in parallel in
src/include/catalog/{meson.build,Makefile}, while before the makefiles
had it in src/backend/catalog/Makefile.

I think keeping the two build systems aligned this way will be useful 
for longer-term maintenance.

(There are other generated header files that are linked in a similar way 
and could perhaps be simplified.  But they don't all work the same way. 
Some of the scripts also generate .c files, for example, so they need to 
put some stuff under src/backend/.  So I restricted this patch to 
src/{backend,include}/catalog/, especially because it would be good to 
keep the catalog lists aligned.)