Re: Add progressive backoff to XactLockTableWait functions

When I first suggested this idea, I used 10s as an example for
the maximum sleep time. But thinking more about it now, 10s might
be too long. Even if the target transaction has already finished,
XactLockTableWait() could still wait up to 10 seconds,
which seems excessive.

What about using 1s instead? That value is already used as a max
sleep time in other places, like WaitExceedsMaxStandbyDelay().

If we agree on 1s as the max, then using exponential backoff from
1ms to 1s after the threshold might not be necessary. It might
be simpler and sufficient to just sleep for 1s once we hit
the threshold.

Based on that, I think a change like the following could work well.
Thought?