pgsql: Rename BUFFERPIN wait event class to BUFFER

Rename BUFFERPIN wait event class to BUFFER

In an upcoming patch more wait events will be added to the wait event
class (for buffer locking), making the current name too
specific. Alternatively we could introduce a dedicated wait event class for
those, but it seems somewhat confusing to have a BUFFERPIN and a BUFFER wait
event class.

Reviewed-by: Melanie Plageman <melanieplageman@gmail.com>
Discussion: https://postgr.es/m/fvfmkr5kk4nyex56ejgxj3uzi63isfxovp2biecb4bspbjrze7@az2pljabhnff

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/6c5c393b74031351721f8a44e55bfaf6f249eefb

Modified Files
--------------
doc/src/sgml/monitoring.sgml                    |  8 +++-----
src/backend/storage/buffer/bufmgr.c             |  2 +-
src/backend/storage/ipc/standby.c               |  2 +-
src/backend/utils/activity/wait_event.c         | 12 ++++++------
src/backend/utils/activity/wait_event_names.txt |  6 +++---
src/include/utils/wait_classes.h                |  2 +-
src/test/recovery/t/048_vacuum_horizon_floor.pl |  2 +-
src/test/regress/expected/sysviews.out          |  2 +-
src/tools/pgindent/typedefs.list                |  2 +-
9 files changed, 18 insertions(+), 20 deletions(-)