Alist of fonts vs the rescaling factors.
Each element is a cons (FONT-PATTERN . RESCALE-RATIO), where
FONT-PATTERN is a font-spec or a regular expression matching a font name, and
RESCALE-RATIO is a floating point number to specify how much larger
(or smaller) font we should use. For instance, if a face requests
a font of 10 point, we actually use a font of 10 * RESCALE-RATIO point.