rcParams['font.size'] is consulted at render time

[tacaswell]

This makes it a bit tricky to show old vs new via rcParams in the documentation.

I suspect this has been this way for a long time, I could argue either way on changing this to be artist creation time now.

[tacaswell]

On a bit more inspection, this is due to the string -> points scaling happening late.

[tacaswell]

Closed by #7007