gh-107570: Argument Clinic: report errors on the offending line (GH-155250)

Errors raised while the docstring is checked were reported on the line
which ends the clinic block, and errors raised while the code is generated
were reported without a file name and a line number at all.

Functions and parameters now record the line on which they are declared,
and the function docstring records where it starts, so that such errors
point at the offending line.