pgsql: Improve TimestampDifferenceMilliseconds to cope with overflow sa

Improve TimestampDifferenceMilliseconds to cope with overflow sanely.

We'd like to use TimestampDifferenceMilliseconds with the stop_time
possibly being TIMESTAMP_INFINITY, but up to now it's disclaimed
responsibility for overflow cases.  Define it to clamp its output to
the range [0, INT_MAX], handling overflow correctly.  (INT_MAX rather
than LONG_MAX seems appropriate, because the function is already
described as being intended for calculating wait times for WaitLatch
et al, and that infrastructure only handles waits up to INT_MAX.
Also, this choice gets rid of cross-platform behavioral differences.)

Having done that, we can replace some ad-hoc code in walreceiver.c
with a simple call to TimestampDifferenceMilliseconds.

While at it, fix some buglets in existing callers of
TimestampDifferenceMilliseconds: basebackup_copy.c had not read the
memo about TimestampDifferenceMilliseconds never returning a negative
value, and postmaster.c had not read the memo about Min() and Max()
being macros with multiple-evaluation hazards.  Neither of these
quite seem worth back-patching.

Patch by me; thanks to Nathan Bossart for review.

Discussion: https://postgr.es/m/3126727.1674759248@sss.pgh.pa.us

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/3a28d78089289794fda86cdbd275fc4756c6c6aa

Modified Files
--------------
src/backend/backup/basebackup_copy.c  |  3 ++-
src/backend/postmaster/postmaster.c   | 11 ++++++-----
src/backend/replication/walreceiver.c | 12 +++---------
src/backend/utils/adt/timestamp.c     | 21 +++++++++++++--------
4 files changed, 24 insertions(+), 23 deletions(-)