pgsql: Create a separate file listing backend types

Create a separate file listing backend types

Use our established coding pattern to reduce maintenance pain when
adding other per-process-type characteristics.

Like PG_KEYWORD, PG_CMDTAG, PG_RMGR.

To keep the strings translatable, the relevant makefile now also scans
src/include for this specific file. I didn't want to have it scan all
.h files, as then gettext would have to scan all header files. I didn't
find any way to affect the meson behavior in this respect though.

Author: Álvaro Herrera <alvherre(at)kurilemu(dot)de>
Co-authored-by: Jonathan Gonzalez V. <jonathan(dot)abdiel(at)gmail(dot)com>
Discussion: https://postgr.es/m/202507151830.dwgz5nmmqtdy@alvherre.pgsql

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/dbf8cfb4f02eb9ec5525de1761675f9babfd30e3

Modified Files
--------------
src/backend/nls.mk | 2 +-
src/backend/postmaster/launch_backend.c | 32 +++---------------
src/backend/utils/init/miscinit.c | 59 +++------------------------------
src/include/postmaster/proctypelist.h | 51 ++++++++++++++++++++++++++++
src/tools/pginclude/headerscheck | 9 ++---
5 files changed, 65 insertions(+), 88 deletions(-)