Show ignored constants as "$N" rather than "?" in pg_stat_statements.
The trouble with the original choice here is that "?" is a valid (and
indeed used) operator name, so that you could end up with ambiguous
statement texts like "SELECT ? ? ?". With this patch, you instead
see "SELECT $1 ? $2", which seems significantly more readable.
The numbers used for this purpose begin after the last actual $N parameter
in the particular query. The conflict with external parameters has its own
potential for confusion of course, but it was agreed to be an improvement
over the previous behavior.